Implement a local cache for cards

[NiloCK]

Fetching a card by id requires three round-trips (the 2nd two in parallel) from the database:

1. request card by id
   • returns id_view, id_data
2. request view, request data
   • return viewName, questionData
   • render the appropriate view with the returned data

This is too slow for fetching to occur between each viewed card. A card cache should exist that stores cards data locally in an associative array, with the id_card as key.

Card loading should check the cache first and perform db lookups when necessary.