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.

If it doesn’t exist it will be prefilled with all registered categories
set to false

Changed settings version as the link configurations must be redone (with the new port names)

Also fixed a typo (copy/paste error) in the TCP link settings loading where it was using the UDP port as the default value instead of the TCP port.

I understand the intent when this was first created but nobody is using it and it no longer fits the context. If and when a need to abstract the serial link comes back, we can revisit this.

Also converted qDebug statements to logging category

I noticed that some times, the disconnect signal would get to the updateConnect button (tool bar) before the link was physically disconnected. That would cause it to count it as a still connected link and get the connect button logic out of sync.
While at it, added an interface to the UDP link to return its configuration instance. That allows the LinkManager to unlink it when disconnecting it.

This came through google groups and as the change is right where I'd been working, I added it here to avoid collision.

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).

There's also a partial fix for the databits and stopbits. I'm unsure how to deal with the logic
around the 'is_cdc' variable, as I can't really follow what it's for.

Now works for more than Serial links

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

Plus a large number of other changes to allow for orderly shutdown of
objects without crashes or asserts. This is need for unit tests to
create/delete global state around every test.