Add default styling for document creator.

[begedin]

Currently, the document-creator component has no styling at all. Since our share-modal does have some default styling, I was thinking we might want to do the same with the document-creator.

Adding styles organized into separate files is quite simple now that I figured out #93 and merged #99.

This is what the document creator looks like at the moment in the TodoMVC:

The background is due to the app styling, but most of the other stuff is just default, unstyled stuff.

I was thinking we could center it on the page and make the coloring and styles similar to that of the share-modal. The styles would be structured around the tag name, the same way share-modal does it.

[venkatd]

Could we make a minimal style for the dialog so the structure and layout is preserved between apps?

[venkatd]

In other works I agree 👍