Add dashboard support for trove replication v1

Note: this is a placeholder blueprint and will be fleshed our as more information becomes available

As part of Juno release Trove will add the first round of support for Database Replication
This is defined in the blueprint:

https://blueprints.launchpad.net/trove/+spec/replication-v1

This dashboard blueprint covers the changes needed in the openstack dashboard to support replication v1 which will include:

1. Allow creation of a slave instance (by specifying the master at instance creation time)
2. Display information about master / slave relationship of instances
3. Detach a slave so that it becomes a standalone database instance