CMS improvements

[shushugah]

Currently only techworkersberlin.com/events collection are update-able with the DecapCMS.

• A similar flow for techworkersberlin.com/news collection would be possible.
• Update decap-CMS to include news collection (relevant code here)
• Use a list widget instead of boolean widget to select our different netlify forms (default, zoom, general, etc..)
• Have a dropdown of tags (used by both events and news...to filter, for example https://techworkersberlin.com/works-councils shows all related events and news articles with the tag works-council instead of the free text, achieve this by creating a YAML file inside (_data)
• Make it possible to update/add press entries (code here)