Use `mattr_accessor` over `self` for module attributes
Move `FeatureFlags` module closer to `InfoFrontend` declaration

This deals with an ordering issue and means we can keep our inialisers
simpler so that they just define the values they need to set.
Merge pull request #23 from alphagov/use-mattr-accessor

Move location of `FeatureFlags` module and use `mattr_accessor`