So no need for connect window close test here

This removes confusion as to whether you call UAS::requestParameters
(incorrect) or QGCUASParamManager::requestParameterList (correct) from
client code.

This allows use of compile time Object::connect syntax

Simple starting point to view testing

This was leftover from a problem I was having with virtual slots

Allows for UI unit tests to be written:
- Ability to respond to expected message boxes
- Ability to fail test if unexpected message boxes occurs

Allows you to run a single unit test from the command line

- 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.