Standardize prop -> DOM attribute process

Allow more than strings and numbers to be used as attributes for DOM
nodes. This removes the special casing for `0` and `false` that was
being used in ReactDOMInput and ReactDOMTextarea.

Now we will just `toString` any object we try to insert into a DOM.

Closes #422, #372, #302
Be consistent with object naming in tests

This also fixes line length issues our linter was complaining about.
Make sure DOM components work in JSDOM
Merge branch 'SanderSpies-sspi-dom-attribute-process'