Bug 849280 - lazyloading of HTML, CSS & JS in the browser app r=benfrancis

shared files fix

lint fix

newline

linting errors

lint

lazy loader tests

lazy load shared css

first time thumbnail screen fix

leftovers

topsites screen fixed

web activities fix
Merge pull request #8548 from michalbe/browser-perf

Bug 849280 - lazyloading of HTML, CSS & JS in the browser app