[Scenario] Enforce constraints when Timeline View created

Enforce the full constraint system for a Timeline View
as soon as the Timeline View is created. This prevents
the user from visualization any nonsensical or
contradictory activity timeline, even if it is
permissible to construct such a timeline by way of
using other composition tools (Info View, create
wizard, drag-drop to add multiple parents...)

This is primarily intended as a quick-fix to
nasa/MCT-Plugins#59 although it also reduces the
practical severity of nasa/MCT-Plugins#42
[Scenario] Fix containment bug

Activity type was incorrectly filtered out of
create menu for Timeline Views; this restores
that option.

Similarly, Activity Timeline was incorrectly
available as a create option in the same
context. This has been removed.
[Scenario] Revert accidental commit

Prior commit accidentally removed unrelated files;
these are restored here.
[Scenario] Merge containment fixes
[Scenario] Save constraint changes

Track components actually touched by constraints,
and invoke save on any which are changed when a
Timeline View is loaded. This ensures that Save and
Save All are available as soon as the view is
loaded, so that those automated changes aren't
lost.
[Scenario] Enforce constraints in scenario view

This begins to adapt the constraint-enforcement
automation employed by TimelineView such that it
is also obeyed (and does not disrupt) the Scenario
View.