switch to generic features

[Gjum]

• should be integrated with the component plugins refactor to isolate components #23
• unified format for markers, polygons, circles, lines etc. like on https://www.reddit.com/r/cvcft/
• collections of features are also features
• tree view of the visible features to create a new collection and configure visibility instead: filters
• export the current collection to pastebin-ish providers or reddit or firebase create drawing on the map and share it #28
• put exported features in url, shorten if too long tracked as separate issue
• import other collections by pasting their url tracked as separate issue

[Gjum]

requirements changed a bit since this issue was created