(bug 45558) Show workflow state selector when needed

* Always create the workflow state selector element, even if
  the group with which the page is initially loaded doesn't need it.
* Hide the element initially. Every time the TUX page is rendered
  with a new group, check if the group has valid states, and show
  the element, or hide it otherwise.
* Change the messagegroups API to return false for workflow states
  of dynamic groups.

Change-Id: I2f7edcec84839926496c70389904244e65405eb1
Merge "(bug 45558) Show workflow state selector when needed"