Add licenses for metric verification

Instead of internal to track different licenses to use for verification
I have added a license file from opendefinition.org which I want to
extend from time to time.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Implement license metric

I have implemented the license metric which counts the number of open
data licenses based on a license file which determines whether a license
is open by the fact if it is OKD compliant or OSI compliant. This commit
closes #11. I have also added the dl-de-by-1.0 license. More additional
licenses will follow.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>