Add Button Indicator On Sign In

[marcaaron]

Problem:

At the moment, when signing in there is no visual indication that the app is trying to do anything at all. This creates confusing UX since you're never sure if you are waiting for something to happen or if something has broken.. and then BAM you get redirected at random.

Solution:

Add a loading indicator inside the button when we have a pending sign in attempt and remove it on error.