Renames default API_EXTENSION_NAMESPACE
Adds checking of normal extensions detected which atm just loads all of them
Copies over core server.py functionality and loads resources/controllers into mapper
Work around no extensions found exception raising with stevedore
Register extensions into core extensions loaded in memory list
Adds v2/tenant_id/extensions functionality as an extension rather than core,
  but in a "core" directory
Adds entry point to allow extensions to extend server create functionality (kwargs to create)
Adds os-keypairs functionality