Issue #7 : Add characters when adding keys

Added importChars() function to EVECredential, which imports all characters
attached to that key.

Whenever a key is added via the GUI, importChars() is called.

Also added "get_or_create" type functions to EVEAlliance and EVECorporation.


My first commit, so please point out things that should be different (coding style or anything).  Also, this is very much back-end. There is a "characters/list.html" frontend but that's for testing so anyone can fix it up.

Also, not sure what details were wanted here. I only store name, corp and alliance. If something else should be stored, let me know.