Timeline: add filter input

I'd say there are many reasons why one would want to filter/search in the Timeline view. If I want to see exactly when I used WhatsApp in the last 4 hours, for example, this view plus an input which filters events accordingly, is probably the easiest option, as long as we don't develop a whole new kind of visualization.

I've already implemented a working concept, but wanted to hear your opinion before I open a PR.
https://github.com/NicoWeio/aw-webui/tree/filter-timeline

There are still some questions:

1. In which .vue file should the input element go?
2. How should items that do/don't match the filter be displayed?
→ I'd suggest greying out items that don't match.
3. Should the aw-server be used for filtering?
→ I guess not, because I'd like to see this implemented as a "real-time search".