Update React JSX Transforms

* Extract JSXDOM into separate transform
* Rename lower case variables in JSX to upper case
* Drop React.DOM docblock, use string tags instead
Rename lower case variables in JSX to upper case

We're trying to move to a convention where lower-case variables on JSX are always HTML/SVG tags rather than variables in scope. See:

http://fb.me/react-jsx-lower-case

Therefore, this diff renames existing uses to upper case variables.

This throws an error on all these files, so I manually go rename all the variables. I then run lint to ensure that the rename doesn't leave any undeclared variables.
Don't use React.DOM

I grepped for uses of React.DOM. This is going to be a set of helper functions
to generate ReactElements without JSX.

They're not classes so they cannot be used where a React class is expected.

Since we always use JSX, we should have no internal use for these helpers.
We can use strings instead.
Start warning when React.DOM.x is passed into JSX

React.DOM is becoming helper factories to generate ReactElements. They're not
classes. It will be ok to call them directly as functions, but not to use them
where a class is expected.