Also added logging category

Check the board description in the LinkManager and display AeroCore instead of Pixhawk for the Gumstix AeroCore board.

Removed redundant counter while at it.

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.

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

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).

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.

Largest change is that once a link is added to LinkManager it maintains
ownership and is responsible for delete. If you need to delete a link
use LinkManager::delete. Also added guard code to assert if a Link is
deleted outside of LinkManager.

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run

Subclass of QMessageBox which re-implements the static public
functions. There are two reasons for this:
1) The QMessageBox implementation on OSX does now show the title
string. This leads to message boxes which don't make much sense. So on
OSX we set title to text and text to informative text.
2) If parent is NULL, we set parent to MainWindow::instance. This
prevents message boxes which can go behind MainWindow

Centralize all connecting and disconnecting of links through
LinkManager::[Connect|Disconnect]Link api. Connect/Disconnect no longer
allowed through LinkInterface. This allows creation of new
LinkManager::setConnections[Suspended|Allowed] methods to disallow
connections as needed.

Changed many functions in the abstract *Link classes to be const. This facilitates setting other functions as const. The metadata for specific links are reset when the links are added.