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

Destroyed signal must have been working incorrectly in the past.

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.

This allows you to determine if full parameter list is ready if you
missed the parameterListUpToDate signal.

This allows you to determine if full parameter list is ready if you
missed the parameterListUpToDate signal.

Handy for testing without a real board

This test is too flaky to run in TeamCity reliably.

Specifically:
- Channel reversing
- Incorrect usage of function and channel index

- Also corrected system/component id usage
- Switched to new Qt5 connect api

Also uses new min/max/invalid widget display

- Updated to use RCChannelWidget
- Removed attitude control widgets
- Previous calibration values now shown when not actively calibrating

Mimic pending param support by just calling through to setParameter.

Added:
- sequence numbers
- better filtering for image encapsulated data messages versus FTP
- directory list now contains file sizes
- open command now returns file size in data

Specifically much better testing for the handling of:
- Ack responses not being sent by server
- Getting Nak’s back from commands
- CRC failures

Also changed file validation to take into account Mock Server no longer
sending file length in first byte of file.

Also changed the downloaded file contents to not include the file
length in the first byte. This makes the code a bit less confusing.

When unit tests are being run in TeamCity the host box can end up being
very bogged down with other builds. So need to up wait time, to take
into account CPUs grinding.

Need to disambiguate from video stream messages