More improvements in request body documentation generation

Rename @DocumentSetterMethods to @DocumentCommand as it now does more.

Take note of @JsonParameter annotation on command constructors and use
these to generate properties to be documented.

Handle array type examples and make @DocumentCommand convert List<T> types
into T[] array types.

Make @DocumentCommand create a bean that can be assigned to underlying type.

!BUG:25422
!TEST: GroupController POSTs and PUTs should now document the members input
parameters; TrackVersionController should npow document its popularity input
parameter.