No need to force them to show

Plus a large number of other changes to allow for orderly shutdown of
objects without crashes or asserts. This is need for unit tests to
create/delete global state around every test.

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

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run

Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

also adds AMSL output in ft

SLUGS has maintained their patches out-of-tree for a long while now.
These will eventually get merged back in, but it'll be easier to evaluate them as fresh commits instead of modifications to this old & dead code, so we'll delete this for now.

This patch fixes a bug that display 0 for distances to waypoint more
than 10km.

Besides that, it also homogenize the naming of the label to
"distToWaypoint" instead of "distToWP". Old configuration files (in
home directory), should be hacked or removed in order to see this
change.

Signed-off-by: Paul Chavent <paul.chavent@onera.fr>

There is no such things as a clicked signal on QWidget. You activate
new UAS from right-click menu.

The connect call was generating debug output to identify that it was
failing. After looking at the code realized that this connect is not
needed. The group box is removed when UASListWidget::removeUAS method
is called.

Second change in the file fixes a crashing bug when the last UAS is
removed. Need to exit the iterator after we modify it.

Right-click menu works cleaner.
Coloring of output text is correct.
Output text now handles all severities of messages.

Altitude splitted to altitudeAMSL and altitudeRelative, speed splitted to airSpeed and groundSpeed. PrimaryFlightDisplay uses airSpeed for FW and groundSpeed for MC.

Replace 9 seperate valueChanged() signals with just 1, and remove the resultant tons of code duplication