- Use pkgconfig on linux to avoid break build on undefineds
Fix DISABLE_GOOGLE_EARTH
Fix broken connect
Fix warning
Remove signal overrides
Merge pull request #1040 from DonLakeFlyer/SignalOverride

Remove signal overrides
Rearrange code and add documentation for perspective code.

No functionality changes in this code, just code clarify improvements.
Remove unusable Radio Control widget.
Fixed bug where 2 widgets were added to the wrong view.
Correctly initialize floats as NaNs where expected.
Remove the PrimaryFlightDisplay from the Planner view as it doesn't make sense there.
Merge pull request #1039 from DonLakeFlyer/ConnectFix

Fix broken connect
Merge pull request #1038 from DonLakeFlyer/DISABLE_GOOGLE_EARTH

Fix DISABLE_GOOGLE_EARTH
Merge pull request #1047 from Susurrus/pfd_init_fix

Correctly initialize floats as NaNs where expected.
Remove the DEFAULT view from QGC's perspectives logic.

It was a poor proxy for better coding around the problem of bad settings or the lack of
settings on first-run.
Refactor MainWindow settings saving on shutdown.

Fixes bugs with savings settings for the window state, theme, UAS-connected view, and low-power mode.
Also removes some unneccesary logic that attempted to handled unclean shutdowns, which I haven't
been able to reproduce.
Removed unused variable.
Remove all unnecessary calls to QSettings.sync().

This function is called automatically when a QSettings object is destroyed,
so is rarely needed to be called explicitly.

There are still some cases where
a QSettings object is passed-by-reference, so there I left the sync() calls as
it's unclear how permanent those objects are and if they'd call sync() before
application shutdown
use new messages to determine orientation image
rename accel calibration images to match steps