R1:f0af27316563

Add FactCursors and application fact datasources

Summary:
- Add PhabricatorApplication. This is a general class that I have grand designs for, but used here to allow applications to provide objects for analysis by the facts appliction.
- Add FactCursors, to keep track of where iterators are.
- Make the daemon do something sort of useful.
- Add `bin/fact cursors` for showing and managing objects and cursors.
- Add some options to `bin/fact analyze`.

Test Plan:
- `bin/fact cursors`, `bin/fact…