Offline Maps: Import/Export fixes

* Export should always be enabled since you can export default tile set
* Fix Select All/None problem

qgroundcontrol: Use qtquickcompiler by default

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

Windows OpenSSL: Use libs which static link to CRT

Split constructor of HeartbeatTimer up in two functions

Previously the first activeChanged signal got lost because it was not connected yet to the LinkInterface which resulted in a link incorrectly shown as inactive.

Fix for vehicle widget bug

Ignoring Jenkins (Linux) 

Making sure the commands are sent to the camera's actual component ID rather than a hardcoded constant.

QGCFileDialog: Specify fully qualified in folder url

Expose VideoReceiver allowing plugins to override it.

Plan, Offline Maps: Support for center map to specified location

PreFlight: Reorganize to retain state

Vehicle recenter takes into account correct viewport

ArduCopter Tuning - Remove Hover Throttle from tuning

Various fixes

ArduCopter: Initial Heli Setup page

Windows Appveyor: Switch to Qt 5.11

Fix compiler warning

Also distinguish Emergency Stop better

This was too confusion to expose since QGC currently does not support ArduPilot terrain tile send.