Flat sharing community

[huberfel]

Problem description
as discussed within #75 we should consider adding option to better support following two use cases:

1. Someone who might want to found a flat sharing community might want to search for a flat or house that suits well for such a purpose.
2. Somone that seeks an open slot in a flat sharing community

Desired Solution
Case 1: <isSuitableForFlatSharingCommunity />
Case 2:

<categories>
    <category key="flat-sharing-community" />
    <category key="collaborative-workspace" />
  </categories>