Cache Manager  "Back" link for "Cache stored images" incorrect

The ```Back``` button link on the ```Cache stored images``` tab is
missing the path past ```zp-core```.
Merge pull request #689 from JimBrown/1.4.6-CacheManager

Cache Manager  "Back" link for "Cache stored images" incorrect
plugin loading refinement

FEATURE_PLUGINS will now be automatically loaded with ADNUB_PLUGINS on
the back end.