De-googleify e-commerce demo

[fzaninotto]

Problem

With the default material-ui theme, the demo looks too much like a Google, and turns some people away.

Solution

Customize the theme for the demo.

before

after

[djhi]

You should use the theme.spacing() function when dealing with padding and margin. It would ensure consistency

[fzaninotto]

The dark theme hasn't changed much but it's still usable.

[fzaninotto]

As for using theme spacing, you're right in theory, but:

1. we currently don't give a way to customize the default theme spacing in the demo, so it's useless
2. There are MANY other components in this demo using numbers for spacing. This would be a day of work.