Fixed bug with DecksPage unmounting proccess.
Fixed bug with DecksPage unmounting proccess.

What was happening was that when the DecksPage was unmounted it thrown
an exception because the remove calls to stores listeners was
undefined. This behavior happened because the calls were wrongly typed,
the correct was to call '.remove()' on these and not to call itself as
a function.

nwsapps/flashcards,nwsapps/flashcards