Added sidebar widget lazy loading + twitter timeline lazy loading

Changed the 'text widget' lazy loading to 'sidebar widgets' lazy loading.
Added an option to only lazy load text widgets.

I hook observers before every sidebar and clear them after each sidebar.
I used undocumented action hooks, but you can find them in the wordpress source code (widgets.php classes)

Added the ability to lazy load twitter timelines.

Tested all the functionality on a live site - it works perfectly in my tests.

Greetings from Iceland ;)