Review Roles enums

[jag3773]

Perhaps have roles based on Flavor and FlavorType

Relates to #135, #212, audio timing files, Lexicon helper files

[jonathanrobie]

I liked Joel's suggestion to let each Burrito Flavor define its own roles.

[jtauber]

carried over from #52:

• add versification role to indicating versification delta file among ingredients (moved to Add versification role #273)
• add documentation about x- roles, in particular for app-specific files among ingredients

[jtauber]

In addition to the two actions above (Mar 18) we need to discuss what else to include.

Discussion to take place in #262.

This issue to track my actions in light of #262.

[jag3773]

Confirmed by Joel and Tim that versification needs to be a role.