Add notes about web servers, fixes #75.
Add status icons
Add labels and labelings (user, ticket) models
Add label show and remove for tickets
Add create labeling from ticket view
Add tests for creating labelings
Add test to make sure we do not remove selectors needed for javascript
Add labelings to users.
Completely remove subagents and needed fields.

Adding subagents was a hack at best. By adding labels we can
give users access at ticket level, using a nice interface that is
clear to everbody.
Show labels in tickets index
lowercase
Label filtering
Add labels to customer view
Add customer ability to view labeled tickets
Fix migration to automatically migrate ACL
Hide labelings when not allowed to create, fix label_ids in
Also clean params
Cleanup
Filter labels
Use ticket or reply permission for attachment permissions