Namespace for all routes to UI into "rails/migrations"

[ka8725]

Move the following routes from -> to:

"/rails/phantom_migrations" -> "/rails/migrations/phantom_migrations"
"/rails/broken_versions" -> "/rails/migrations/broken_versions"
"/rails/schema" -> "/rails/migrations/schema"

The gem should not pollute the "rails" namespaces with too many routes defined on it as this increases chances for collision with other gems.

Also, the gem should be able to define the entry point (namespace) for all web routes - there should be an option/config for it, default value = "rails/migrations".