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
(cherry picked from commit d7f7c66a3f296e32a095393cd767022819fc102f)