Namespaced view names and templates.

This prefixes all view names with "hk_" and puts all templates under a "hyperkitty" path. This helps avoid conflicting names, for instance both HyperKitty and Postorius have a "user_subscriptions" view name, so if both are installed the actual URL returned for that view depends on the order they are listed in the main settings.  (This is especially problematic for "user_subscriptions" which returns a full page in Postorius but an Ajax-targeted snippet in HyperKitty.)