rose config: document --meta-key=KEY consistently.
metomi/rose#13: rose suite-run: Rose/Cylc version.

Export Rose and Cylc version in `rose suite-run`.
* As environment variable.
* As Jinja2 variable.
* Document in `log/rose-suite-run.conf`.
* (--reload mode should export version of current run, but this is not yet handled.)
metomi/rose#13: rose.run: extend new mode check.

Fail if new mode is specified with reload/restart run mode.
rose suite-run --reload: export old Cylc version.