Give spelling metric first finishing touch

With this commit the spelling metric works so far. It should be clear,
that the metric is far from being applicable. I will need to create a
personal dictionary to extend the list of correct words. This commit
closes #6.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Refactor compute method to return record score

I have implemented the better class design for the metrics. Instead of
using an instance method/attribute to store and retrieve the score for
a given metadata record the score is returned immediately through the
compute method itself. This fixes #42.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add score meter to the repository show page

The score meter to display the overall score is added with this commit
to the repository show page. I am not quite sure yet where to store the
function to create the score meter as I will need to access it from the
metric show page as well.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Improve layout for the score meter

Just added some changes to improve the score meter's positioning.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add score meter to metric show page

Now the score meter is displayed at the metric show page as well. The
only thing left is to color the score meter based on the reached score.

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