implements the first part, working for configured variants;
for that, loading of stylesheets was overhauled by now
merging all configured variants into one big stylesheet for
each output format and loading this instead of one stylesheet
per configured variant;
previously @media print styles were applied on top of @media screen
styles; this is now strictly isolated, which doesn't require styles
like neon to revert styles for print anymore;
this change was also used to implement the minify parameter, to shrink
those generated stylesheets, making them shrink to 66% of their
unminified size for the exampleSite;
the theme switcher functionality is now completely independend of
variant.js; the switch is now handled by in-page javascript which
avoids waiting for external scripts to load, so switching can happen
as early as possible;
switching of themes is now implemented by just setting a data attribute
to the html element, were previously a complex mechanism of dynamically
loading of variant CSS files was implemented;
the call for variant.js was removed in this changeset, making the
generator broken and useless; this will be fixed with the next patch;
