feat: Filter for the showcase items.

[dploeger]

This features a filter for the showcase items as described in #210

The filter looks like this:

It can filter the title, type, platform and tags by using the filter UI and also by using the query params like this:

/showcase?title=dung&tags[]=narrative&tags[]=rpg#showcase

I guess, we should ask the developers what tags they would like to use. This is currently just a bunch of tags I thought would fit.