Added Backlog model
Convert old team->backlogpool to backlog->team model
Move Scrums migration to checksetup.

Also allows just deleting the old tables
Pool add/remove_bug methods to accept ID as they used to
Move page handlers out of Extension.pm
Fix User->agile_teams for users which are not in any group
Add option to create backlog with a team
Backlog mangement in Team editor

* Webservice methods to create and update backlogs
* UI controls
Fix uninitialized value warning
Updated readme about Scrums migration
Adapted scrum planning for multiple backlogs

Use three panels in a carousel for sprint, backlogs and unprioritized,
two of them shown at the same time.
Remove date buttons from sprint edit dialog
Move unique name check to Pool object
Allow changing the case in Pool name
Fix remove role list update