added test case for validateSharing in versions API
added tests for buildXML of membership API
added tests for create and update of issue category API
added tests for addWatcher and removeWatcher of issue API
fixed removeWatcher in issue API
added missing covers annotation and test case
added test case for TestUrlClient
added test for cleanParams and create of issue API
added test for update of issue API
Merge pull request #73 from JanMalte/unittests

added some more Unittests to reach higher code coverage