Remove instance varables and handle null data

The tab instance variables are never used, we always use the optiions
object.

Handle the cases where there are no completions on a graph and where
there is no data coming back from backdrop.

Also remove extra comma on the end of collectionAttrs object.
Update backdrop stubs to match new requests
Update tests for new completion collections

As the number and rate collections don't contain any real logic any more
remove all the tests execpt those which check the methods they house.

Rewrite the completion collection tests now that there is no date logic
as most of the old tests are redundant.
Remove unused date functions

None of these are used any more after the completion rate graph has been
refactored.