Make groupings functionally equivalent to groups

Groups and groupings (i.e. groups of groups) should be functionally equivalent, in the sense that anywhere you can filter or select by groups a grouping should also be allowed.  It makes no sense that both are treated as completely different beasts.

Allowing to use groupings everywhere a group can be used would immensenly increase the flexibility in managing students while also simplifying it. See MDL-59092 or MDL-69806 for just two examples.