Replace stylesheets/shared.css with ke/css/khan-site.css

Summary:
stylesheets/shared.css was an out-of-date minified copy from the same
source as ke/css/khan-site.css, so to simplify perseus, all references
were replaced with references to khan-site.css.

Test Plan:
Visit test.html and testrender.html and ensure that the hint buttons
look like we'd expect for .simple-button.orange, and have the correct
fontawesome trash icon.

Auditors: alex
Transformer: highlight the currently selected tool button

Summary:
Adds more contrast between the currently selected tool and the
not-selected tools.

Test Plan:
Visit test.html
Add a transformer widget
Click on Translate/Rotate/Reflect/Dilate
Do they turn a nice bright blue?
yes -> yay
no -> this commit is broked

Auditors: eater