This does a few things:
* Change from button list to a select combo box.
** This allows users to type the number they want
* Add the ablity to tag versions to releases
** E.G. Say mitaka was released with 2.27, it will
show in the list as "2.27 - Mitaka".
** This currently set as a config option in
conf.py as a dict like:
os_api_ref_release_microversions = {
'2.27' : 'mitaka',
'2.10': 'liberty'
}
* Uses https://github.com/danielfarrell/bootstrap-combobox
** Apache Licenced
Change-Id: Ica7dd55cdbf413f03ea635aefb627a705132a73e