Additional ProgressStore implementations

[olliestanley]

Currently we have a SimpleProgressStore which serializes a map of progression to a file. This probably isn't ideal and actually is more there so that we can test that everything else works which depends on storage.

Other options:

Human readable:

• XML
• YML
• JSON
• SQL (MySQL, SQLite)

Not human readable:

• BSON

[olliestanley]

XML is stubbed atm, but that's it

[olliestanley]

This is basically priority as this is all that's stopping Questy from being complete

[olliestanley]

We have a simple store now which serializes a Map to a file