Sidebar cosmetic fix, and first time load bug w/ view_size

First, sorry about the messy diff -- some lines were unchanged but for changing tabs to spaces -- I'm happy to re-request without. It seems like there isn't really a convention and various places used tabs and others spaces.

Two changes here:

1. A fix to the sidebar so that it doesn't scroll with the content pane.
2. A fix to a bug where visiting mailpile for the first time (without a view_size set in localStorage) screws up padding on basically everything since it doesn't use the default.