PhEDEx improvement

Refactor the code to use WMBS as the source of information
instead of opening specs, this allows better accounting and
flexibility.

Summary of functionality changes:

- Clean up the SQLite code in PhEDEx, it is outdated and not supported.
- Add the Tier-0 support through the safeMode option.
- Check for duplicate dataset subscriptions before subscribing, this included unapproved transfer requests.
- Requests are compacted by site and datasets (i.e. some requests will subscribe multiple datasets to multiple sites if possible).

Fixes #4479
Fixes #4480