Designate version of helium-theme add-on the editor is built for

[web-devel]

Problem

The editor is actual for the particular version of the Helium add-on (latest release). For earlier versions there may be some discrepancies e.g. in variable names which will confuse users.

Suggested solution

Display version of the Helium which is currently used in editor. Potentially leave instruction how to run editor for previous versions