Generalize group by method for accessibility chart

For GovData.de I can use the metadata original portal, but for all
others I am using the group now. Often the group encodes the data
provider, too. At least more or less.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add test for richness of information

This test should ensure, that a record with more relevant fields does
not automatically score a higher result than a record with only few
relevant fields. In every case the score needs to be averaged.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Start to refactor test and implementation of RoI

I have started to refactor the richness of information metric code and
test. This includes to extract a lot of the code into separate methods
as well as distinguishing between free text and categorical fields.

As part of this I have added a value method which retrieves a value from
a hash based on a dot-notation which I have used in the recently added
accessibility controller, too.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Remove too simplistic test

I removed a test which expected a pretty concrete floating-point number
where it was not clear from where this number comes. Besides the fact,
that the test will break in the future I do not think it helps much
anyway.

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