Slow migration of $processid to $taskid

[rsoika]

Since version 4.3.2 we support the new item "$taskid" which is replacing the deprecated item "$processid". See #383

Because of the fact that many process instances with only the $processid will still exist we can not remove the deprecated field or ignore it over a long period of time. For that reason we do a slow migration of the field in two phases:

Phase I.

After more than one year from now on, we will add first a warning message into the methods getTaskID and also the finder methods of the DocumentService and LuceneService if $process id is used.

Phase II.

After much more than 2 years from now on, we can drop the method setProcessID() and getProcessID().

After all we will still support processInstances with the field "$ProcessID".