Simplified button style declarations

These are now pretty specific and several types and sizes of buttons are
available. Further reuse should be easy to implement whenever CSS
preprocessors are made available.

Some notable style changes have been done too, but the core idea is having
more reusable components.
Cleanup: removed tabs
Cleanup: use 2-space indent
Use url template tag
Simplified evernote_auth CSS
Set event handlers in JavaScript

Also there's no need for extra asset files and removed global variables.
Use 2-space indentation, i18n love
Stretch contents/sidebar up to the max height