Triggrs: Makes Logical triggers construct OK

The logical triggers now need their sub-trigger(s).  The functionality
has been fleshed out (but not yet tested).  The logical trigger tests
now properly include sub-triggers.

TEST=unittests pass.
Triggers: Adds Not test, improves debugging, fixes arm bug.

The NotTrigger has additional testing.  It's still not complete.

Really improved the printouts for debugging.  Adds __repr__, indents
stuff, changes text to make clearer what's going on.

LogicalTriggers weren't arming themselves properly.  That's changed
here.

TEST=unittest (including new ones).
Trigger: Adds a NotTrigger test.  Passes test.
Triggers: Fixed OrTrigger logic, adds tests for OrTrigger

Passes tests.
Trigger: Fixes bug in AndTrigger, adds tests for AndTrigger.

Passes all unittests.
Triggers: Tests now include trigger arming/disarming.

TEST=unittest - passes all including new ones.
Trigger: Added handling for 'arm' and 'trigger' messages.
Triggers/Executive: cleans up a bit, adds |register_timer_handler|.