Add a rating to extensions based on how well they follow best-practices

We currently list all addins. Some of them very outdated. We should either define a minimum version which they need to be compatible with or mark outdated addins clearly as outdated.

Suggested criterias for rating:
- Supports latest Cake version (Builds against recommended Cake version or newer) / Weight 10
- Works with all runners (Targets recommended .NET version or multi-targets) / Weight 9
- Has cake-contrib as co-owner / Weight 9
- Has alias category set / Weight 8
- Contains XML documentation / Weight 7
- Is hosted in cake-contrib org / Weight 5
- Has repository metadata / Weight 3
- Has license metadata / Weight 1
- Has icon embedded / Weight 1

Out of scope:
- Works cross platform (partially this is handled by target .NET version, but we can't rate if implementation works cross-platform)