Add filters for facet fields / content types #90
Description
Check out https://songs-search.typesense.org/
After typing a query, when the initial results appear, there is a sidebar on the left where you can filter by fields like release date and artist. With the help of InstantSearch.js widgets, we can pretty easily add something similar for ImageJ. Just need to figure out what the facets are going to be, and how to make widgets that allow filtering by different collections (wiki vs. github vs. gitter vs. .... all the different buttons from the old search.imagej.net).