Merge pull request #397 from cvan/potatohoudini

ensure that hidden screenshot thumbnails are never loaded (bug 983346)
new splash screen; use minified splash-screen stylesheet (bug 966051, bug 965925)
use vendor prefixes for old flexbox for iOS/Safari WebKit (bug 966051)
load image when visible on detail page (bug 983346)
bold things by default
do not use background-size shorthand for incompatibility banner (does not work in iOS WebKit)
use localStorage to store API responses (bug 980081)

* use localForage instead of localStorage
* add tests
* enhancement for later: move background XHR to a web worker