Greetings, Orgmoders.

After some discussion with Yantar on IRC, I humbly submit the attached diff
for your consideration.

It adds new hooks to org-info-js to allow the following: 1. inserting
page-specific HTML into each OrgInfo header, and 2. calling a custom
JavaScript function to run after any page navigation button/link is
clicked. I have used these hooks to implement Org-fleuron, a custom config
with nice navigation buttons, a greeting balloon, and embedded theme/fonts.
You can find out more about org-fleuron here:
https://davidotoole.info/fleuron.html?#org5dc18bc and the page was made
with the setup.

I also corrected some of the English messages displayed by org-info-js.

I hope you will find this useful.

Please let me know if you have any questions or comments!