Also additional major Mission usability changes

The overloaded member signal just hit us, to use it is a pain
but the resuting code is faster and less error prone, so it's
still a good thing to do.
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

There are many ways of iterating over lists in C++/Qt.
In the specific case of QStrings, it is known [1] that using
foreach with const references avoids the creation of new
QString objects in each iteration, reducing the time consumed
by the loops.

[1] https://blog.qt.io/blog/2009/01/23/iterating-efficiently/Signed-off-by: Anselmo L. S. Melo <anselmo.melo@intel.com>

This commit introduces the APM Airframe configuration. The interface
is the same as the PX4 one, but the way we deal with the uas is a bit different

Since the APM stack doesn't provide a xml with airframe definitions a
new one was created by hand with only the values that we need, wich will
trigger a download of the parameters file from the mavlink github

Now it correctly handles the FRAME variable and it's faster
regarding the download of the parameters for each type of Frame.

Only show Airframes for ArduCopter, not for ArduRover nor ArduPlane
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

I think the assert caused boot crashes at some times

- New mission command editor dialog
- New MissionCommands toolbox object to get command info
- Added APM mission item set

Instead us a Toolbox concept which hangs off of QGCApplication