add back favicon
add logo icon to upper-left corner of notebooks and control panel
Merge pull request #359 from twosigma/spot/icon

Spot/icon
Move code-cell behaviors according to design

Implements a basic version of the codecell styling
that does not remove any functionality however brings it closer
inline with the implemented design.
Remove side click behavior from codecells
Move right cell menu according to new design.
Add a test for showing the codecell menu
Test toggling a code cells visibility
Move cell menu items into top level header
Update style of the new cell indicator.
Test expanding the newCell menu
Update dropdown menu styles.
Update new app header styles.
Add a compile task for scss
Replace app.css with app.scss
Add a watch task for dev
Split up styles into modules
Ignore npm-debug.log
Add cell indent level indicator.
Add loading indicator to codecells