Make use general methods in the spelling metrics

I have applied some refactoring. For instance, the value method used by
the Richness of Information metric to retrieve values from a metadata
record by using an accessor path has been moved into the metric parent
class.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add unit test for the spelling metric

I have added a unit test for the spelling metric in order to make sure
the refactoring works as intended.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Refactor spelling metric for store analysis data

I have refactored the spelling metric in order to implement the storage
of analysis information in the metric computation.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Refactor metric computation URL to REST command

The POST request to start a metric computation is now issued through a
REST command as well. I think I will go back and use one POST request
for one computation.

One computation means one repository and one metric. After all it is
questionable to start so many computations anyway. Although with few
Sidekiq workers this can work smoothly, too.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
List misspelled words only once

In order to store the misspelled words only once per field I have added
an additional method invocation to uniq. Also the enumeration starts now
with one and not with zero.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Display the analysis results nicely in a table

For the generic metric report view I have added tables to represent the
analysis results. The accessor path is formatted by removing the square
brackets and the colons. For each field the individual score is shown.

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