Merge pull request #107 from VWoeltjen/mctPlugins103b

[Scenario] Clean up UI for Activity Type's info view
[Scenario] Revise time editing in Info View

For activities in the Info View, keep
duration constant and shift other times
as needed when adjusting start or end
time, as requested in nasa/MCT-Plugins#110.

Additionally, avoid validating that
start is less than end, as the shifting
behavior means this is no longer
relevant (and refusing to do so makes
it hard to move an Activity farther
into the future.)
Merge pull request #116 from VWoeltjen/mctPlugins110

[Scenario] Revise time editing in Info View
[Scenario] Rename visual control for links

Rename ActivityTypeVisualControl to
LinkVisualControl, in preparation for
reuse of class as a part of the visual
control for Activity components.
(Supports nasa/MCT-Plugins#103)
[Scenario] Add link control to Activity info view
[Scenario] Support URL in Activity custom control

Adds wrapper class used to communicate URL
(in addition to existing tag-like categories)
between Activity Component and its custom
control in the Info View.
[Scenario] Add URL field to Activity model

Adds field to store external link in
Activity model and connects this to
user interface in the Info View.

This completes amendment of solution
to nasa/MCT-Plugins#103 to include
links on Activity objects (not just
Activity Type objects)