single _doRender() error doesn't break all future _doRender()'s

Before, if a single component threw an error in `_doRender`, Plottable would no longer render anything ever again. That's silly, other components should render just fine.

Now an error will not affect other components, and the component will continue to be retried until it renders without failure.

For QE, try checking out my branch and adding `render_error.js` to `list_of_quicktests.json`. I didn't want `render_error.js` to be a regular quicktest because it produces a bunch of errors. 

Close #728.