[Refactor] Moved shortcut for showing help to mod_help
[Refactor] Renamed 2 functions
[Refactor] Moved `isRtMouseButton` to mod_contentHelper
[Refactor/Feature] Moved the feature to search selected search quickly on any search engine into new module mod_quickSearchSelectedText

- (and enabled this previously commented out feature again)
Merge branch 'master' of https://github.com/MakeBetter/Units

Conflicts:
	content_scripts/mod_help.js

[Moved the feature to search selected search quickly on any search engine into new module mod_quickSearchSelectedText]