Cleaned up commits and code + fixed some smaller stuff

Added caching mechanism, like this the plugin can be run in a
production environment (if desired) without slowing down the page.

The changes speed the plugin up significantly (~60 files takes about
1.8 seconds on every page rendering, with new code it's down to 0.04s
and if something is changed around 1s)

Check for usergroups before running the plugin. Prevents it from
executing when visitors watch the page and when manager users with no
rights to change element files reload the pages

Added debugging possibilites including speed measurement.

Cleaned up the commit mess and mad one out of 6 =)…sorry, that was just
pasted in directly on github when adding the features^^
Fixed the descriptionkey_desc array key
Fixed an error with / combining and did some tidying up
Shortened the length of the log lines a little bit
Added check for empty file lists so no unnecessary work isn't  done. Also stops log lines for element classes that don't actually contain any elements.
Turned off debug, maybe it would be best to have that as a system setting?
Updated version number and readme