Dark mode for wallet

[dariatarakanova]

Color specification:

1) Background on all pages - #000000 (rgb 0 0 0) 2) All text boxes - rgb 20 20 20

3) Color for colorful button's text and icons - rgb 28 28 30

4) Gradient at the top of screen - should have opacity 85% from current colors

5) Titles H2 + transaction comment text + dates on transaction screen + comments (besides send and receive screen) - should be rgb 142 142 147

6) Shadow under alert should be - rgba 0 0 0, 0.4

7) Alert box color - rgb 28 28 30 Separator's color - rgb 72 72 74

8) Action sheet background - rgb 44 44 46

Screen examples here: https://app.zeplin.io/project/5c73dc8aa74b4b4085a86a91/dashboard?seid=5dbc2700e1948c239ca23fd8

Icons with new color here: https://zpl.io/aR9Og8v

[gingervik]

@Denis-Asipenko QA will not check it - approved