add touch method to timestamp behavior
automatically set refreshTimestamp on set

If a user sets the timestamp, but refreshTimestamp is truthy, the set
value will effectivley be ignored
remove new checks

If the entity is new and touch is called expicitly, it is probably more
logical (and removes a chunk of possible cases where the method returns
false doing nothing) for the field values to be bumped. Also makes the
code slightly simpler
Merge pull request #2406 from AD7six/3.0-timestamp-touch

Implement Timestamp touch