add and remove operations for fund associations with users and compute sites

Changes include new controllers, a bit of routing, an adjusted view, two model methods and some locales.
Believe it or not, this is actually correct grammar (and perhaps a fitting example of how political correctness can screw with the language ;). "Them" is sometimes used in relation to a single person when the person's gender is not known. I personally prefer this syntax to the somewhat pretentious "him/her".