Configure the Related Events block to accept tags

After some consideration and testing, this has been reworked to the following rules:

1. Any featured/sticky events
2. Any event(s) matching the tag(s) for the current page, in chrono order
3. Events that do not match tags on the page will not be shown (as they are not “Related”)

We’ll call this new functionality the “Tag” type of filtering. As per the existing functionality, “Upcoming” and “Locations” will still be options. Both will also surface “featured” events and then proceed as per their prior functionality.