Not properly showing with dynamic previewing

[jacob-g]

Steps to reproduce:

1. Go to settings -> editing and enable "Show previews without reloading the page"
2. Edit a page with scratchblocks
3. Hit "Show Preview"
4. Change the content blocks
5. Hit "Show Preview" a second time
6. Notice that the blocks did not render

Solution:

Trigger a render when live previews are generated. A hacky solution would be to just add an event listener to the "Show Preview" button, but a better solution would be to see if there are any JS events fired or something. MW documentation seems to indicate there is a "wikipage.content" hook we can use.

Example code from MW for the hook is:

mw.hook( 'wikipage.content' ).add( fn ).remove( fn );

[jacob-g]

It appears we do properly use the hook and the function is running. Adding a delay (via setTimeout) seems to make it load properly, so maybe we're somehow triggering too early?