Optimize PNG images via zopflipng to save size

[PeterDaveHello]

Recompress the PNG images losslessly, to help deliver a smaller app, save bandwidth, storage and downlod time.

 app/src/main/res/drawable-hdpi/arrow_down.png                | Bin 478 -> 313 bytes
 app/src/main/res/drawable-hdpi/arrow_up.png                  | Bin 466 -> 296 bytes
 app/src/main/res/drawable-hdpi/bg_drawer_header.png          | Bin 59292 -> 51751 bytes
 app/src/main/res/drawable-hdpi/ic_settings_black_18dp.png    | Bin 380 -> 360 bytes
 app/src/main/res/drawable-hdpi/ic_turtle_active.png          | Bin 522 -> 313 bytes
 app/src/main/res/drawable-hdpi/ic_turtle_black.png           | Bin 720 -> 410 bytes
 app/src/main/res/drawable-hdpi/ic_turtle_default.png         | Bin 552 -> 388 bytes
 app/src/main/res/drawable-hdpi/line.png                      | Bin 253 -> 164 bytes
 app/src/main/res/drawable-hdpi/transmission.png              | Bin 1825 -> 1480 bytes
 app/src/main/res/drawable-mdpi/arrow_down.png                | Bin 338 -> 227 bytes
 app/src/main/res/drawable-mdpi/arrow_up.png                  | Bin 387 -> 241 bytes
 app/src/main/res/drawable-mdpi/bg_drawer_header.png          | Bin 33123 -> 29459 bytes
 app/src/main/res/drawable-mdpi/ic_settings_black_18dp.png    | Bin 256 -> 253 bytes
 app/src/main/res/drawable-mdpi/ic_turtle_active.png          | Bin 386 -> 244 bytes
 app/src/main/res/drawable-mdpi/ic_turtle_black.png           | Bin 512 -> 311 bytes
 app/src/main/res/drawable-mdpi/ic_turtle_default.png         | Bin 418 -> 279 bytes
 app/src/main/res/drawable-mdpi/line.png                      | Bin 222 -> 135 bytes
 app/src/main/res/drawable-mdpi/transmission.png              | Bin 1296 -> 1101 bytes
 app/src/main/res/drawable-night-hdpi/bg_drawer_header.png    | Bin 41066 -> 36657 bytes
 app/src/main/res/drawable-night-mdpi/bg_drawer_header.png    | Bin 24122 -> 21827 bytes
 app/src/main/res/drawable-night-xhdpi/bg_drawer_header.png   | Bin 55095 -> 48581 bytes
 app/src/main/res/drawable-night-xxhdpi/bg_drawer_header.png  | Bin 84136 -> 73115 bytes
 app/src/main/res/drawable-night-xxxhdpi/bg_drawer_header.png | Bin 98482 -> 83696 bytes
 app/src/main/res/drawable-xhdpi/arrow_down.png               | Bin 554 -> 369 bytes
 app/src/main/res/drawable-xhdpi/arrow_up.png                 | Bin 576 -> 376 bytes
 app/src/main/res/drawable-xhdpi/bg_drawer_header.png         | Bin 82474 -> 71964 bytes
 app/src/main/res/drawable-xhdpi/ic_settings_black_18dp.png   | Bin 453 -> 440 bytes
 app/src/main/res/drawable-xhdpi/ic_turtle_active.png         | Bin 624 -> 361 bytes
 app/src/main/res/drawable-xhdpi/ic_turtle_black.png          | Bin 917 -> 497 bytes
 app/src/main/res/drawable-xhdpi/ic_turtle_default.png        | Bin 726 -> 493 bytes
 app/src/main/res/drawable-xhdpi/line.png                     | Bin 285 -> 195 bytes
 app/src/main/res/drawable-xhdpi/transmission.png             | Bin 2375 -> 1869 bytes
 app/src/main/res/drawable-xxhdpi/arrow_down.png              | Bin 804 -> 545 bytes
 app/src/main/res/drawable-xxhdpi/arrow_up.png                | Bin 754 -> 520 bytes
 app/src/main/res/drawable-xxhdpi/bg_drawer_header.png        | Bin 91921 -> 77113 bytes
 app/src/main/res/drawable-xxhdpi/ic_settings_black_18dp.png  | Bin 628 -> 610 bytes
 app/src/main/res/drawable-xxhdpi/ic_turtle_active.png        | Bin 884 -> 459 bytes
 app/src/main/res/drawable-xxhdpi/ic_turtle_black.png         | Bin 1396 -> 678 bytes
 app/src/main/res/drawable-xxhdpi/ic_turtle_default.png       | Bin 1200 -> 678 bytes
 app/src/main/res/drawable-xxhdpi/line.png                    | Bin 359 -> 246 bytes
 app/src/main/res/drawable-xxhdpi/transmission.png            | Bin 3514 -> 2565 bytes
 app/src/main/res/drawable-xxxhdpi/arrow_down.png             | Bin 1037 -> 710 bytes
 app/src/main/res/drawable-xxxhdpi/arrow_up.png               | Bin 935 -> 670 bytes
 app/src/main/res/drawable-xxxhdpi/bg_drawer_header.png       | Bin 111481 -> 93084 bytes
 app/src/main/res/drawable-xxxhdpi/ic_settings_black_18dp.png | Bin 827 -> 796 bytes
 app/src/main/res/drawable-xxxhdpi/ic_turtle_active.png       | Bin 1140 -> 567 bytes
 app/src/main/res/drawable-xxxhdpi/ic_turtle_black.png        | Bin 1841 -> 856 bytes
 app/src/main/res/drawable-xxxhdpi/ic_turtle_default.png      | Bin 1535 -> 856 bytes
 app/src/main/res/drawable-xxxhdpi/line.png                   | Bin 463 -> 318 bytes
 app/src/main/res/drawable-xxxhdpi/transmission.png           | Bin 4417 -> 3235 bytes
 app/src/main/res/drawable/transmission.png                   | Bin 1296 -> 1101 bytes