Move away from inline styles

[othree]

Hi

I saw #439 have one task is "move away from inline style".
I am totally support it. So I raise this issue with following reasons:

Current attributes-kit uses inline style for every component.
Which is bad for server side rendering and is very hard to customize style(theme).

For server side rendering. Most inline styles are the same.
Duplicated style declarations increases the size of result HTML file.
And inline style has very high priority. Also make its very hard to overwrite it.
Also, there is no class name for people to customize style now.

I am willing to contribute.
But I think this kind of change requires some discuss before send PR.

[othree]

Maybe we could have two separate change for this:

1. An options to disable all inline styles
2. Add classname for each components

Which don't break current inline style structure