Fix metadata retrieval bug

With the GovData.de repository I receive no metadata when executing the
metadata method on the repository object. It seems one reason is that I
used the term call from the Tire DSL.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Use JavaScript to perform repository selection

In the metrics overview it is cumbersome to press the button every time
a repository is selected. Hence, I have added a small event listener to
shorten this step. This commit closes #16.

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