Show the link indicator in the tool bar if two or more links are connected and at least one of them is a high latency link.
Show in the link indicator if a link is inactive.

- Improve function names
- For notifications of an active link change only show the priority keyword if multiple links are connected
- Use QMap instead of QList for the HeartbeatTimers
- Style improvements
- Simplify sending the MAV_CMD_CONTROL_HIGH_LATENCY command

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.

Each link updates the active property based on incoming bytes.
The vehicle tracks the active property of each link and in case of an inactive priority link it updates the priority link.

This reverts commit 52160d80.

Prevent shutdown ordering crashes

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

Obligate LinkInterfaces to implement getLinkConfiguration. 11ab9aa0 introduced a bug where TCP links would cause a crash loading the sensors page

This mechanism automatically queues data into the correct thread where necessary, otherwise the method is invoked directly with low overhead.

At the same time remove the UDP socket event workaround. It is not a problem.

Plus other auto connect bug fixes

Windows OS doesn’t disconnect port when you pull plug on USB. This
caused all sorts of problems with previous logic. New logic handles
this correctly.

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

Link ids were being used interchangeably with the mavlink channel for
the link. Link ids handed out as a numerically increasing integer. Once
the counter went past MAVLINK_COMM_NUM_BUFFERS all hell would break
loose and cause memory corruption.

Also many LinkManager API changes to further isolate all link
management inside LinkManager.

The goal of this first installment is to organize the code a bit so it's more readable,
clean up a bit of left over cruft, and manage link configurations (and links in general).

Moving methods from MainWindow to QGCApplication so that more things
can run without a window. Helpful for testing.

Fix linux compiler warning