[#3] Make PATCH to collections work like entities

- Created PatchCollectionInputFilter; isValid() method sets the validation group
  on the input filter for each iteration of a data set, raising an exception if
  an error occurs when adding the validation group.
- Altered ContentValidationListener to create either a
  PatchCollectionInputFilter or a CollectionInputFilter based on whether at
  PATCH or other style request is being made.
[#3] Allow POSTing collections

- Allows POSTing many entities at once, and properly validates them now.
  The REST service will need to detect if an array of data is present,
  or a single entity.