Bootloader improvements.
Bootloader improvements.

- Cleaned up includes.
- Replaced flash_leds() with toggle_leds().
- Improved start_app().
- More debug prints during update process.
- Performing readback verify after each sector write.
- If the verify of the app's vectors fails, then that sector is erased
  to prevent the app from booting.
- Comparing the firmware.bin file size with the size in its header
  before starting update.
- Flashing LEDs while waiting for card to be removed or inserted if
  there is not a valid app.

flit/modular,flit/modular,flit/modular,flit/modular,flit/modular