ACT-1418 Unit tests and suggested fix for NPE on uncaught error event

Work done at Hackergarten Vienna together with @rafacm and
@florianpirchner
Docs for ACT-998 + added script execution listener
Merge with master
Merge branch 'ACT-1418' of https://github.com/pebrc/Activiti into pebrc-ACT-1418
Merge branch 'master' of github.com:Activiti/Activiti
ACT-1555: accepted 2 pull-requests, tests now fixed
Added Camel task to user guide
Merge branch 'master' of https://github.com/Activiti/Activiti
Fixed ACT-1362: Support for UUID as JPA @Id type
moved xsd's to converter project + added missing modules to distro build
Merge branch 'master' of https://github.com/Activiti/Activiti
Accepted part of pullrequest #24: Serializable for test-compound JPA-ids
Act-1465: documented services in user guide. This introduces the service API sooner in the user guide such that new users can get started better.
ACT-1574: Added loopcharacteristics to subprocess
Merge branch 'master' of github.com:Activiti/Activiti
Merge branch 'master' of github.com:Activiti/Activiti
ACT-1568: doc fix on native queries
ACT-1505: Should throw an exception if the picture is not generated: added extra logging
Fixed issue with script engine resolving
Merge branch 'master' of https://github.com/Activiti/Activiti