BaseView.rendered was set after onInitialRender() completed, but

before onRender() completed. This could be a bit non-intuitive, and

limited what information onRender() had available. We now set this

after onRender() completes.
This also adds two new events: rendering and rendered. Both take an

object parameter with an initialRender boolean. Consumers can listen

to this to perform actions pre/post-render, making it easier to perform

actions at the right point in the render stages in a consistent way.

Unit tests pass.
Made use of the new signals in some in-progress work.