upgrade QC + Rails 4 + db lock page + NULLS LAST when sorting

This is a WIP and requires a bit of testing before merging.

Those are breaking changes.

Includes:
- [x] upgrade to QueueClassic 3
- [x] upgrade to Rails 4+
- [x] adds a page to see db locks for the process running a job
- [x] make the null show last when sorting 
- [ ] ...?