Do not use Fragment#getContext()

Fixes: 33457680

-getContext() was causing crashes on L.
-Also call HistoryAdapter.setEvaluator() in
HistoryFragment.onActivityCreated()
-Remove mCurrentExpressionDescription and just use the resource id

Change-Id: Ie88c4a80d162d5719627bb3cac4afc4ceef7caf1