Save more ram flash + fix some bugs

[bl-ackrain]

• Remove float to save flash space.
• Remove unused variables to save ram.
• Fix Screen mode 1.
• Remove all the warning.
• Fix currentFile buffer overflow.
• Buttons in polling mode, dac write and backlight are not using mbed any more.

Galaxy Fighter goes from: Flash: 93% RAM: 82.5% to: Flash: 88.4% RAM: 78.9%