Define docs structure, add missing docs

[davidknezic]

We currently still use the old Web Style Guide structure of the docs. There's lots of docs we can remove, because they are not technical, meaning that most of the Fundamentals and Patterns part will be obsolete.

Building the header and revamping the layout, I thought about using a two-part docs structure. The first part would be presenting our components and describing their usage in a readable way, as Bootstrap does. The other part would be a generated one, perfect when searching for plugin options, scss mixins, variables or utilities.

What do you think about this? @elessar-ch @FKSI @AndyOGo @sventschui @carlosdelsol @kawtar01?