Fix/default font family

Hi, I'm new to the project and want to contribute. :-) I'm currently getting myself antiquated to the code base.

I noticed that the fonts in the frontend are inconsistent:

screenshot

It seams that there was 'Open sans' used at some point in the project, but currently no external fonts are configured.

This pr:

removes the references to 'Open sans' (as it is not loaded anyway)
configures the same default font-family at 2 places: \src\semantic-ui\site\globals\site.variables \src\styles.less
it tweaks some font-sizes and paddings a bit to get a similar look as before

After the pr:

grafik

openbikesensor / portal