[Scenario] Add Procedure URL to Activity model

Add a field to store a procedure's URL
to the model of Activity. This supports
nasa/MCT-Plugins#131
[Scenario] Add visual controls for Procedure link
[Scenario] Add padding around Activity links

Add a few pixels of padding around Activity
links shown in its Info View.
Merge pull request #148 from VWoeltjen/mctPlugins131

[Scenario] Add link to Procedure in Activity