user-requested metadata fields for project detail page

[moedn]

• repo host
• project active/not active anymore (would be possible using the dashboard
• missing instructions (would be possible when deploying ODRL (→ already available in the backend see https://losh.ose-germany.de/wiki/Property:P5372))
• rebuilds count, popularity (data not available from most repo hosts; would require a dedicated backend if deployed by LOSH)