Add Twitter Bootstrap

I have added Twitter Bootstrap and Sass dependencies to the project and
started to improve the styling in a custom Sass file.

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

I have refactored parts of the application layout content into a footer
and header partial by using Rails' render command.

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

Currently I am planning to implement a control panel for the different
metrics. Hence, I have generated a metrics controller currently with a
page giving an overview of the metrics.

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