Improved error message if a reference cannot be resolved while executing
a rule or script

Signed-off-by: Oliver Libutzki <oliver@libutzki.de>
Added possibility to load dynamically added action classes at runtime

Signed-off-by: Oliver Libutzki <oliver@libutzki.de>
Merge pull request #31 from OLibutzki/Bug437756

#437756: Dynamically added action classes cannot be loaded at runtime