editor_main: improve gamemodestopper

[sacr1ficez]

• Replaced bound element to predefined resourceRoot
• Used startedResource from parameters instead of method call getThisResource()
• Loop isn't called anymore when resource can't stop other resources (missing perms)
• Also it's no longer in it's scope (perm check)
• Replaced ipairs with better equivalent
• Improved readability

[jlillis]

Requested changes minor and optional - I think this is good to merge in a few days as-is if nobody else has blocking comments.

[sacr1ficez]

@jlillis done.