Add multi-tag filtering on Resources page

[tomspilman]

We have a bunch of tags on the Resources page:

Currently you can filter by a single tag. This is ok for now, but i expect eventually we'll need more complex "searches" for resources.

To get a more complex search using tags, multi-tag filtering would help.

We would have to work out the details of how you multi-select them. Toggle them on/off? Shift+click?

[JakeLegendXIII]

I have made an attempt to do this on #238 if anyone wants to check it out or provide feedback. I implemented it using Shift+Click with a button for Clearing All. The current iteration allows for falling back to the route based filtering, but defaults to the new multi-tag filtering when you first land on the /resources page if nothing else is at the end of the link (like /resources/2d/).