Maintenance - use dom.js module instead of globals

With the Issue Reporter we have introduced a dom.js module that contains commonly used $ and $$ function to query the DOM.

TODO

• remove every call to the global E(id) variable, replacing it with $(#id) instead
• use $ and $$ instead of document.querySelector and document.querySelectorAll
• delete function E(id) {}
• verify if it makes sense to normalize $$ to return an array so that common operations such for/of and forEach are possible in every browser we target, including Chrome 49