Support for WakaTime clients #125

I really thought there was already an issue about this, I remember I've been thinking about it for a long time. Thankfully @Stefano_Agazzi reminded me.

WakaTime is great, it collects useful data which you can get meaningful insights from. Unfortunately, it has a proprietary server-component. Luckily the mechanics are similar so it would fit pretty well with ActivityWatch. This would make building a bridge or modifying a WakaTime client a lot easier than writing custom plugins for one/every editor.

We've actually had WakaTime-like features in mind for a while now, so here are two possible options:

1. We've learned a lot from how they do things in the past, so modifying WakaTime plugins to work with ActivityWatch shouldn't be too much work.
2. We could build a bridge or API which acts as WakaTime would but really used ActivityWatch as a server and user interface. This could avoid having to make any modifications to the clients, essentially just a configuration change (proxy config).