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>
Removed redefinition of PYTHON var in makefiles

Also fixed some typos in some makefiles.

Signed-off-by: Francesco Nero <nerofrancesco@hotmail.com>
GCS coreplugin:avoid loading each configuration twice on startup
GCS systemhealth:Only display missing elements warning once
Merge pull request #1129 from francesconero/next

Fixed make/firmware-defs.mk to use PYTHON env variable
GCS:uavgadgetinstancemanager renamed loadDefault to forceLoadConfiguration
GCS:uavgadgetmanager selectionActivated refactored

listSelectionActivated renamed to doReplaceGadget
selectionActivated not a Slot anymore
GCS:uavgadgetmanager added doxygen to recently changed functions
GCS:uavgadgetmanager made selectionActivated public
Merge pull request #1147 from guilhermito/GCS_enhancements

Gcs enhancements
Fixed PNG files to remedy error "iCCP: known incorrect sRGB profile"
logview: always pickle the framed log data for faster reload
GCS:connectionmanager make device a smart pointer to prevent crashes
GCS:main fixes the redraw of the spashscreen on some systems
uavtalk.py: format data correctly for overo logs too
Python: convert timestamps to seconds

The log files all use millisecond for the timing precision. This
converts to double seconds when unpacking this value into the
UAVO itself. This format is much more convenient for any analysis
and being a double avoids nasty effects when visualizing as
time.
logview: delete large obsolete variable to reduce memory footprint
Merge pull request #1149 from solidgoldbomb/python-logview-speedup

logview: always pickle the framed log data for faster reload
Merge pull request #1150 from guilhermito/gcs_fixes

Gcs fixes
logview.py: do not attempt to append null objects

If an object UAVO is not known, then it is appended as a null
which breaks hte iteration through the tuples.