- Adds a new interface, Apper, that enables loading and persisting
  instance-level data in new ways
- Converts some initialization funcs to methods
- Exports funcs and methods needed for intialization
- In general, moves a ton of stuff around

Overall, this should maintain all existing functionality, but with the
ability to now better manage a WF instance.

Ref T613

Now the func takes a username and password instead of a single string.

This exposes setup and admin functions in the writefreely package, and
uses them in the main application, initialized by the flag parsing that
now happens there.

This is the first step towards making `writefreely` usable as a
standalone package.

Includes app config and some initialization