Timebox Kanban

Adds the ability for the current Kanban Board App to detect if the custom page has a timebox filter.  When the filter is set to `None`, the app works the same way it works today.  When `Iteration` or `Release` is selected, the board appends the timebox query to the user's query filter.

Also adds the selected Release or Iteration reference to the Add New button.

I would love to write tests for these changes, but I don't have a dev environment set up where I can deploy these changes to test against.