Add setOrCreateTextParameterValue

To share logic with StringParameterValue, add setOrCreateParameterValue.
Add option for selecting encoded string for multiline text parameters or not.
Add test for readableMessage
Fix some issues

* Increase IGNORE line number for checkstyle
* Missing import
Merge pull request #141 from rinrinne/freetext

Store plain free text to GERRIT_CHANGE_COMMIT_MESSAGE