Comms: Slightly modify the modality change to Comms Dialog

Setting the dialog as modal makes it appear as a ‘slide panel’
and this looks wrong on OSX
Log Download: Robustness improvements on log download
Log Console: fix SIGSEGV
Joystick Widget: Upgrade to SDL2
Joystick Widget: Revive joystick code

Configure your joystick through the joystick menu.
Activate the joystick (so it sends events to the UAS) by clicking on the joystick name.

If the UAS is a multi-rotor in stabilize mode, the joystick controls are sent as RC overrides, otherwise if the UAS is in manual mode the joystick controls are sent as manual controls.
Joystick Widget: Fix button pressed events not showing up in the UI
Joystick Widget: only emit joystickChanged at 10Hz if the joystick hasn't actually changed
Joystick Widget: use explicit calls load()/store() to compile under Qt5.4
Build: Fixes for compiling and installing with SDL2 for Windows and Linux
configuration: Update to beta 2.0.15-rc5
Compass View: Add fix for compass calibration with DEV_IDs in use
Compass View: Add compatibility mode for compass calibration pre-AC3.2
Full Param Setup: Add EEPROM format fix for APM:Copter
Log replay: Fix for crash when loading tlogs, and another when tlogs stop playing
Control Widget: rename member variables (code review)
configuration: add a default directory for missions (flight plans)
Mission Widget: fix waypoint save dilaog not appearing
Firmware Loader: Fix for px4 PID misdetection
configuration: update to RC6
ComboBox Control: Fixes #522 combobox and layouts effected