Run key generation in a worker

Ground work for a smoother registration flow. Overall UX still needs
some polish but at least now we can have a progress gif or animation or
whatever. Also adds the phonenumber-confirmation step as a simple alert
box, which will be replaced with a nice dialogue in a later commit.

libtextsecure/protobufs.js

@@ -1,7 +1,7 @@
 ;(function() {
 
     function loadProtoBufs(filename) {
-        return dcodeIO.ProtoBuf.loadProtoFile({root: 'protos', file: filename}).build('textsecure');
+        return dcodeIO.ProtoBuf.loadProtoFile({root: '/protos', file: filename}).build('textsecure');
     };
 
     var pushMessages     = loadProtoBufs('IncomingPushMessageSignal.proto');