Fixes#3562.
Second part of the two-part special with #3772. When Keyman
Configuration starts, it creates a task that is launched whenever a
specific Keyman event with id 256 is added to the Event Log. This task
launches keyman.exe to start Keyman (and if Keyman is already running,
the newly launched process will exit with no side effects).
This feature is behind a new feature flag `Flag_UseAutoStartTask`, so it
can be disabled in the event of compatibility issues.
The task is created or updated on each launch of Keyman Configuration
(or Keyman via the 'Keyman' shortcut in the Start Menu), and is
intended to be self-maintaining.
The test_starttask project (4 of the 12 files) is just a wrapper around
the start TKeymanStartTask class to allow for manual testing. No unit
tests for this at this time; I think it would be difficult to unit test
this effectively.
