Add support for Datastores to Trove dashboard

Gerrit topic: https://review.openstack.org/#q,topic:bp/datastore-support,n,z

Addressed by: https://review.openstack.org/75269
    Initial support for datastore in Horizon

[2014-03-10 mrunge] I'd like to see a bit more, what is planned here.

[2014-04-09 michayu] See below:

Added datastore type and version columns in Instance Table
Added datastore type and version in Instance Details
Added appropriate Connection Examples (for each datastore type) in Instance Details

Patchset #16+ has single dropdown approach with the following behavior:
- Auto select only if there's one datastore type and version
- Otherwise, enforce user to choose one
- Single dropdown uses optgroups to group versions for each datastore type

Patchset #15 has double dropdown approach with the following behavior:
- Initially, only the datastore type dropdown is shown
- If there is only 1 datastore type, it will be auto selected
- Once a datastore type is selected, the datastore version dropdown will appear
- Datastore versions will be populated dynamically per the datastore type chosen
- If there is only 1 datastore version, it will be auto selected
- Last chosen datastore version (for that datastore type) will be saved when switching between the various datastore types

Trove community decided (in weekly meeting) to go with single dropdown approach (at least for now). If most providers generally start having many datastore-types and many datastore-versions for each datastore-type, then we can revisit the double dropdown patchset.