Add back ability to convert personal journals to communities

* under /communities/convert (no redirect from the old page); looks like
  /communities/new

* also tweaks success_ml to expect a scope instead of a message ml
  (.success.title / .success.message are now expected to be set in the
  scope's .tt.text), and to fit in the foundation style
Merge pull request #753 from afuna/convert-journal-to-community

Add back ability to convert personal journals to communities