Store empty contraint parameters as null values as "" is not a valid constraint value.

 This allows you to link Annotated actions to Share forms.
Register dummy actions to populate the action list.
Upgrade Felix fileinstall to 3.2.6 (still had issues with ConcurrentModification)
Merge branch 'fridael'
Merge pull request #41 from laurentvdl/master

Alfresco Actions