Adds APIVersionRequest class for API Microversions

Adds the APIVersionRequest class which handles converting the API
version requested from a request header string and supplies
comparison and matching methods used by microversions and REST
API code to determine what code paths to take.

Partially implements blueprint api-microversions

Change-Id: Ic75d36fc0d27b615e70e1fe56c1626e9e501b1d6