Widget themability check

[tomdye]

Enhancement

We should take time to check how themeable the widgets we have created really are.
A popular style of web components that people often like to use is material. A good way to test the themeabilty of our components would be to have a go at creating a material theme.

[dylans]

Rather than doing material at this time, why don't we go through this process and create a Dojo 1 flat theme for Dojo 2's widgets ( see comments at dojo/examples#275 )... this will improve interop with Dojo 1 and also verify that this is working as it should.

[tomdye]

I think the reason for Material was that it is a little more complicated that the dojo 1 flat theme and thus a better test of the theming system. I understand your point though.

[tomdye]

This is covered in the material epic #615