Enforce integer processing versions

This extends the support in WMWorkload and WMTask to include a
processing string along with the processing version and acquisition era.
The processing version is now enforced to be an integer
in the reqmgr and the lfns are built as following:
```
<acquisitionEra>-<processingString>-v<processingVersion>
```

The job reports contain all these three elements for each output file
however the DBSBuffer will only use the processing version and acquisition era.

Fixes #4007