Add a custom parameter value for Base64 encoded string

Fix for JENKINS-23421
tore encoded GERRIT_CHANGE_COMMIT_MESSAGE into custom parameter type

Fix for JENKINS-23421
Fix test
Merge pull request #160 from rinrinne/custom-parameter-value

Add custom parameter type for Base64 encoded value
Update to filter ChangeKind in PatchsetCreatedEvents

ChangeKind is now exposed by Gerrit, which gives Jenkins the ability
to filter for changes that are trivial rebases or changes that do not
impact code.
Merge pull request #159 from vangdfang/master

Update to filter ChangeKind in PatchsetCreatedEvents