Properly cache on a per-user basis

This will fix an issue with templates of other users being applied to
different users logged in. Basically the first cached page would be
displayed for all users.

Created a new cache key for smarty to allow the user ID to be reference
in the cache key. Hence each user has their own cached file which will
be used.

Improved caching by creating subdirectories for cached files. This way
we won't run into a file limit per directory with a lot of cached files.

This fixes #430 and the mentioned issue in that report.
fixing smarty cache key generation
Merge pull request #442 from TheSerapher/issue-430

Issue 430