Return existing tag from Ticket#addTag(...)

If the added tag already exists instead of throwing
Add tags migration
Fix re-adding deleted tags
Update README.md
Extract Discuss from TicketView #123

And add stub for TagEditor. TicketView is now tab view for various
ticket related sub views.
Fix double write in devmode
Fix empty domain
Move handlers adding from modal to tab
Remove unread icon for now

Not implemented by the backend currently
Extract TicketCollection from models.server.Ticket
Remove visibilites filter from withUnreadComments
Clean up /api/tickets test
Add follower filter to /api/tickets
Display all followed tickets on the frontpage
Just end the response on proxy fail

Calling next on this situation crashes the server...
Do not add handlers tag anymore

We now just use the followers query (/api/tickets?follower=3)
Send notifications about new tickets #122

to a given email address
Extract EditableList from AttachmentsForm
Configure forwardTicketsEmail from Ansible
sadf