Tachyon: Set favicon for heatmap pages

[StanFromIreland]

The JS is not ideal, but I think it's better than duplicating the image.

[pablogsal]

Thanks 🖤

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86 Debian Installed with X 3.x (no tier) has failed when building commit 2db9573.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1244/builds/6896) and take a look at the build logs.
4. Check if the failure is related to this commit (2db9573) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1244/builds/6896

Summary of the results of the build (if available):

Click to see traceback logs

fatal: unable to access 'https://github.com/python/cpython.git/': Could not resolve host: github.com

chmod: cannot access 'target/': No such file or directory

make: *** No rule to make target 'distclean'.  Stop.

[StanFromIreland]

Thanks 🖤

Thank you for merging! I was finding the titles a bit annoying to navigate since it was just a file path, it'll stick out now.