Move the heatmap outside the sidebar

Inject the heatmap into the host frame using the default embed script.

It will be possible after this to make vanilla embed codes available
which can be used for headless operation or inserting the heatmap in
guest frames.

Fundamentally, the heatmap is altered to behave as though it's inside
the same frame as the annotations. That makes it easier to access
the highlights directly, rather than the pre-resolved jquery that
was being serialized across the bridge before.

Since it is now necessary for the reply counts to be known outside the
sidebar, the bridge is changed to support updating annotations and the
sidebar application is changed to bubble updates through ancestors.

Since iframes cannot have visible overflow the z-index constraints
required to have the heatmap still appear attached to the sidebar
dictated that the controlbar move outside as well.

Lastly, I took this opportunity to improve the up/down buckets with the
help of the jquery scrollintoview plugin, which should ensure that
this function works even in situations with nested scrollable panes.

Also, closes #464.