Offline Maps: Allow custom build settings overrides

TODO: Improve the experience

Add QGC_DISABLE_INSTALLER_SETUP to CONFIG will override config in QGCInstaller.pri.
However, QGCInstaller.pri can be imported in the custom one. In this way
a custom build can generate it's own installer config or add pre and post steps.

ArduPilot for configurable mavlink stream rates

On desktop (Ethernet connection), the ground unit pushes UDP directly, which makes the use of an actual "Link" not possible. Instead, I've moved all of Taisync support to a "manager" owned by QGCToolbox.
Added a Taisync settings with some basics already wired and running.

Expose guided altitude settings. Rearrange Fly and Plan view settings.

FW Landing Pattern: Support for stop photo/video. Plus item unit test.

Fix xcode project and restore LaunchImage
Cleanup unused icons

Fix xcode project and restore LaunchImage
Cleanup unused icons

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Add the HeartbeatTimer class to track a single heartbeat for a single link.
For every new received heartbeat an instance of the class is created.
Every instance emits a signal if it timed out or the timer is restarted.
Each vehicle then decides based on all different signals which link is the
priority link.

The build system will look for src/Airmap/Airmap_api_key.h
If it find is, it will used the provided API key and client ID for Airmap.
That file should provide two strings:
static const char* kAirmapAPIKey = "key data";
static const char* kAirmapClientID = "id data";

Local builds, without these will have no Airmap support by default (users can always enter their own within the Airmap settings panel).

It builds clean but the resources still get messed up (loads true qml files instead of dummy ones, and it crashes...)

Make all argument to AirMap queries based on what the screen shows (bounding rectangle and/or radius), respecting the limits imposed by AirMap.

Moved flight planning away from "Flight Management" to its own class. Planning does not need a connected vehicle.

AirspaceManager is now exposed by QGroundControlQmlGlobal instead of Vehicle (available all the time)