Previously, stopping exploration could drop info for states processed after cancellation was requested.
There still is a bug where LtsEditor erroneously cancels exploration and does not restart it if React decides to run the useEffect cleanup, but now, the LTS is not broken in that case.

(It was never un-broken with BS4, so that's fine!)

Model checking

See merge request !42

Allow for multiple lines in the TextEditor to be highlighted

See merge request !43