Version checking in rose-stem

To allow control of rose-stem suites with Cylc 6 (which isn't backwards compatible) we need a way of making sure the version of the rose-stem command and the suite both match (see #1375). I haven't received any complaints about this, so I guess this can be merged.

@matthewrmshin would you mind reviewing when you get chance?
Should have spaces before and after `%`.