ENH: Show min-width warning in tour and edit mode

Summary

Introduce a warning that is shown in tour and edit mode when viewed on small screens (#194 (closed) ).

Focus

The warning elements and the toggling have been added to tour.js and edit_mode.js.

Test Environment

Simply open and close the tour while reducing the window size and check that the warning appears if and only if the tour is open on small screens. Log in and verify the same for the edit mode.

Check List for the Author

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