Default role -> Predefined role

Greetings,

Attached is a patch to move from 'default role' terminology to
'predefined role' in the documentation. In the code, I figured it made
more sense to avoid saying either one and instead opted for just
'ROLE_NAME_OF_ROLE' as the #define, which we were very close to (one
removing the 'DEFAULT' prefix) but didn't actually entirely follow.

This would only apply to HEAD, and we'd use the doc redirect + doc alias
features of the website to prevent links to things like /current from
breaking and to provide a smooth path. In the back-branches there would
be a smaller update that just notes that in v14 'default roles' were
renamed to 'predefined roles'.

Compiles and passes regressions, and I didn't find any other obvious
references to 'default roles'. Where I did find such comments in the
code, I opted generally to just remove the 'default' qualification as it
wasn't really needed.

I had contemplated calling these 'capabilities' or similar but ended up
deciding not to- they really are roles, after all.

Thoughts?

Thanks,

Stephen