Some Fixes (#48 and #48) and a new extension point

Hi,
as you saw I added also the above mentioned issues ( #47 and #48 ) and kindly ask you to pull them into master branch.
Additionally I added an extension point to react on model changes in an issue, such that I can reflect some 3rd party logic with an external Eclipse Plug-In not polluting the central code. This 3rd party logic is in our company i.e. to set the assignee to the current user if the state changes to "IN PROGRESS" or if a bug is changed to "SOLVED" the solving user must set an Resolution Attribute. In almost all cases it would be set to "fixed" (amongst other solutions as "Can not reproduce", "Won't fix" or such) and exactly this is what I want to do automatically by a 3rd party Plug-In!
It would be nice to integrate this fixes and feature into the your master branch.

Best regards
Stefan