Add cohbmshelper

There is an entity called 'backing-map-scheme' that exists in a few
different types. This entity would be singleton except its use is very
limited to the top level cache schemes. Overall, the use of this entity
is to refer to one of a few different choices of scheme. It makes more
sense to add the choices of this entity to the types that need them
directly.

This commit includes a helper module that will create the proper
components in a provider to manage the settings of the
'backing-map-scheme'.