removed `&$this` Close #16
Merge pull request #18 from cfoellmann/this

removed `&$this`
use dashicon in the menu directly
condition the addition of js code to admin_head by calling the add_action on "load-" of the networks admin pages
rebase fix + added @since for new function
Merge pull request #17 from cfoellmann/limit-js-output

Limit js output