Adjust login form elements to align to keylines

[mattmiklic]

Form fields in the login flow don't align to the 16dp and 72dp keylines as well as they could. We should take a closer look at form fields in the login flow to ensure that they align. The most obvious example is the WordPress.com password screen, where the two fields aren't vertically aligned.

Additionally, we should check to ensure that icons are being displayed at the correct size. By default these icons should be 24dp, 16dp, or 12dp. The current size seems to be somewhere in-between.

This screenshot shows, from left to right: the current design, the current design with a keyline overlay, and the new proposed design.