SHDP-418 Enhance container groups allocation model

- Replace AnyGridProjection, HostsGridProjection and
  RacksGridProjection with DefaultGridProjection which
  knows how to mix/match wildcard, hosts and racks.
- Introduce concept of AllocationGroups which is a foundation
  of allowing do automatically use different priorities
  for allocation order to support different mixing of anys,
  hosts and racks. This also changes requested allocation
  priority to be a base priority and further real priorities
  are calculated automatically.
- Change yml config model so that projection and its data is
  much easier to use and extend in a use case from Spring XD.