Create SVG library file to store SVG styling

SVG styling like filters or gradients need to be reused. The SVG linking
seems only to work in Firefox, Opera and maybe Safari. In Chrome it is
simply not implemented yet.

There is an open ticket since January 2012 so it does not seem that this
will be implemented anytime soon. For now I will dynamically add it to
every page with an AJAX request.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Refactor and redesign histogram chart

I have refactored and redesigned the histogram chart. This way I removed
the redundant code. I spent a lot of time in styling the histogram. It
looks pretty well now.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Use h3 and h4 elements to describe dashboard

I really should use h3 and h4 elements to describe each dashboard. This
makes also sense from the semantic point of view. I need to adjust some
styling though. There was still a margin in h3, this will affect other
pages, too.

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