Clean up references to MainRootWindow globals

Added a transmitOnly flag to UDP config. When enabled, the socket receive buffer is set to zero such that no data is ever received. Also updated the MavlinkSettings page such that new config settings respect the setting visibility.

Updated mavlink forwarding implementation to forward all mavlink messages received on all channels onto a single UDP port. A new mavlink forwarding UDP link is created if forwarding is enabled. The mavlink settings page now has a Fact checkbox for enabling forwarding and a fact text field for specifying the host name.

Fix textRole usage for QGCComboBox

Fixed flight widget position.

Grouped logging options within General Settings

ArduPilot for configurable mavlink stream rates

ArduPilot option to not start mavlink streams

Fixed the core MAVLink receiver. Among other things, it wasn't accounting for fragmented messages.
Fixed code that monitors messages received (and lost)
Added a section within the MAVLink panel to show the current status (for the current vehicle)
Remove some old, unused exposed interfaces

This reverts commit 52160d80.

Shows horizontal/vertical scroll indicators

Moving source files into Vehicles as it is a more coherent place.

Forcing QGC to use Mavlink V2 if vehicle supports it.

_finalize methods need information which is not available if all you
have is a mavlink_message_t