Add flatpackage conditionals
    
    This will allow us to create python36 easily once needed [1].
    It shoudl also make it easier to merge stuff between python36 and 37.
    
    This more or less backports:
    
    https://src.fedoraproject.org/rpms/python37/c/63459d7d2a4a8df39f900d753cf742c979b480a9
    https://src.fedoraproject.org/rpms/python37/c/7f3ae64d2f98f00b8778b9693ad37fa3c295f4dc
    https://src.fedoraproject.org/rpms/python37/c/6a6d4a03245c076ec8686b8f96ac4ffd3f6ad4e4
    
    [1] https://fedoraproject.org/wiki/Changes/Python3.7