SAS and PA activation reworked, 0.90 compatibility

Initial changes to how SAS is activated, updated PA interaction with SAS. Incorporated some of commit "0.90 SAS fixes".
Assorted bug fixes

Bugs fixed include:
  * SAS not updating when using keys.
  * PID values initially shown on Stock SAS GUI.
  * "CONTROL PAUSED" shown when PilotAssistant is not active.
  * Activation mode not retain on SAS mode switch.
  * Setting vertical speed switches of the wing leveller.
  * Renamed "Max Deflection" to "Max Deflect" as to not overflow on the GUI.
  * PID values not shown on SSAS GUI.
Small change from commit "SSAS updates properly mostly"