Move {{Schema.FORCE_LOAD_KEYSPACES}} and {{Schema.FORCE_LOAD_KEYSPACES_PROP}} to {{CassandraRelevantProps}}

Schema.FORCE_LOAD_LOCAL_KEYSPACES_PROP and Schema.FORCE_LOAD_LOCAL_KEYSPACES should be moved to CassandraRelevantProps for two reasons.

1. Generally speaking, this is where these kinds of things live.
2. By having them in Schema, you can't actually use Schema.FORCE_LOAD_LOCAL_KEYSPACES_PROP without running all of the static initializers... and you want to use Schema.FORCE_LOAD_LOCAL_KEYSPACES_PROP to set the system property before the static initializer runs.