CUNY Academic Commons

I've made the necessary changes. https://github.com/cuny-academic-commons/cac/commit/795a558678c1263e2a52017d1dfe5727b594d323

Here's a summary of what I did:

1. Removed our mu-plugin, added the distro version of the plugin, and enforced that it should be network-activated, using our current standards.
2. Reviewed the changelog for our fork. A couple of the changes over the last 5 years are no longer necessary due to changes in MPO (such as the redirect behavior here https://github.com/cuny-academic-commons/cac/commit/96ac1dc3a34d188630242669df4b2b166f022a51#diff-c45d30312d3e8de61bb4ed8883793f57). Others, I put into a new mu-plugins/mpo-mods.php file.