Today we decided to rename Nimble project
since it's same as a Cinder driver name.
The new name of this project is called Mogan.
For convenience of reviewing, this is a part one
which includes api-ref folder.
Change-Id: Ie1f5bc9d29efcdf77c2b981d6102c56490e70022
Partially-Implements: bp rename-nimble-to-mogan
