Inactive heavens are not properly filtered

[Ingo-FP-Angel]

La Reunion is inactive but still shown on the angels homepage.

I think the line

if 'exists' and 'active' in heaven: 

should be

if heaven.get('exists') and heaven.get('active'):

Right now, the build.py just checks that the key in the YAML file exists and doesn't care if it's true or false.

[StefanBrand]

As a workaround, active can be removed from the heaven's source.