The global shortcuts were removed in favor of key events
which are only triggered when a widget has focus. This is
necessary to allow different widgets to react differently
to the 'enter' key. The current key configuration is:
search edit focused:
  * left/right: decrease/increase card count for selected database card
  * enter: add selected card to deck
  * ctrl-enter: add selected card to deck sideboard
  * ctrl-left/right: decrease/increase card count in sideboard for selected card

database focused: the same as with search edit.

deckview focused:
  * left/right: decrease/increase card count for selected deckview card
  * enter: increase count for selected deckview card
  * delete/backspace: delete selected card from deck

renamed filter list modules to filter tree to more accurately reflect
the nature of the data structure.

filter builder takes filter options from user, then adds
completed filters to the filter tree. the filter tree does
not currently do anything. in the future it will filter the
cards in the database view.