fix(developer): improves More Help link for icon tool

Fixes #2750.

This tweaks the More Help link to open the correct part of the Keyboard
Editor help page. Goes together with keymanapp/help.keyman.com#526.

The context help data needs a consolidated rewrite. This does not
attempt to touch that, nor does it attempt to add more contextual help
links for any other part of the Developer IDE. That is work for another
day...