Added camera initialization code, added comments

- added initCameras function, enuring that camera are on and in last
know mode and running state at each reset
- commented constants and functions in defs.h and main.cpp
Refactored application to conforms to FCOEV2 library changes

- added explicit pause after calling switchOn
Refactored user switch related code, added takeoff detection


Takeoff detection is performed using a switch  a switch with
pull-up resistor

- renamed USER_BUTTON_PIN to USER_SWITCH_PIN
- Added takeoff detection using a switch with pull-up resistor
TAKE_OFF_SWITCH_PIN define in pins.h
Refactored altitude limit related code

- constants have been renamed to be altitude independant
Updated flight phase loop 0 code, refactored flight phase pause
related code

- flight phase loop 0 behavior has been updated
- flight phase pause constants have been renamed
Added debug messages during setup