Use jekyll-include-cache plugin to reduce build time

[cotes2020]

Type of change

• Improvement (refactoring and improving code)

Additional context

Resolves #1094

How has this been tested

• I have run bash ./tools/test (at the root of the project) locally and passed

[jakerr]

Thanks a lot for the quick turn around!
One thing I noticed trying to use include_cached too broadly is that if the included template references any dynamic data that is different per page but not included in the arguments to include_cached, such as the template referencing post.* it will break the pages since they'll all be sharing a cache. (It's mentioned in the README for that project.)

That's why in my example I limited it to the one expensive template which I know was completely static across the site.

[cotes2020]

I missed that point, and it seems that I need to modify the previous commit.