Stop ask to re-link forever

Clear the registration flag when we detect that our credentials have
been invalidated, but retain the knowledge that we've been registered
before, so as to preserve post-first-install behaviors like skipping the
introductory install screens, and accessing the main ui.

Fix #541

// FREEBIE

js/options.js

@@ -21,7 +21,7 @@
                     el: $('#install'),
                     deviceName: deviceName
                 });
-                if (bg.textsecure.registration.isDone()) {
+                if (bg.textsecure.registration.everDone()) {
                     view.selectStep(3);
                 }
                 view.$el.show();