DRY common apipie param descriptions into param groups

Often there are the same params (or majority of them) on some actions,
typically `create` and `update` on resource. New apipie-rails supports
extracting this kind of params into param_group.

Also, params thare are required on creation, are not required, on
update (only can't be nil). `:action_aware => true` achieves this.
Merge pull request #1644 from iNecas/apipie-dry

DRY common apipie param descriptions into param groups