Fixed make/firmware-defs.mk to use PYTHON env variable

It caused build errors on systems where python points to python3.

Signed-off-by: Francesco Nero <nerofrancesco@hotmail.com>
python uavtalk: fix usage of 0 (NULL) rather than "None"
python logview: remove debug code
Removed tools entries that are duplicated in tools.mk
Added missing Windows path export
Fixed error message on non-Windows environments
Add button, change save to file button name
Merge pull request #1140 from larsjohnsen/fix_make_preserve_error

Fixed make error on non-Windows environments
Merge pull request #1141 from metropt/add_clearLog_button

Add button to clear log
GCS:Telemetry Schedular, create a fill with value dialog
Shared:Create sessionmanaging UAVO
Flight uavobjectmanager:Created new UAVObjectCount function
Flight uavobjectmanager: added session managing functions
gcs:added sessionmanaging uavo to uavobjects.pro
GCS uavobjectmanager:Refactored to use Qt's containers.

Renamed some functions to keep so they can be used as legacy if needed.
TODO:Check legacy functions use troughout the gcs to see if they can be refactored
GCS uavobjectmanager:Added unRegisterObject function
UAVObject:Added instanceRemoved signal
UAVObject:added requestUpdateAllInstances function
GCS UAVDataObject:created isPresentOnHardware setter, getter and signal
GCS telemetry:Hooked up telemetry to use the newRequestAllInstance signal