refactor: header and sidebar data passing logic

[lihebi]

Major changes:

1. refactor the logic of data passing in Header and Sidebar. Most code was introduced in #116
2. use {children} for passing items into Header. Relevant code introduced in #152
3. move sidebar to the right. This is not meant to be a better UI, but for the ease of implementing the toggling behavior correctly.

Minor changes:

1. make ui-web/ and ui-desktop/ import styles (App.css and index.css) from ui/
2. remove max-width, partially fix #506
3. remove button:focus styles