docs: renaming gluon-luci-privatewifi into gluon-luci-private-wifi

docs: fix literal blocks

This gets us an up-to-date alfred (and batman-adv 2014.x, as soon as we start to
support it).

The only packages we use from this repo are haveged and (now) fastd and its
dependencies, so we can make the switch safely without updating OpenWrt itself
to Barrier Breaker yet.

It's much nicer to fill in the release notes piece by piece as v2014.4 is
developed, so let's start with the new modular config mode.

docs: add private WLAN

check_site.sh and site.sh were setting GLUON_SITE_CONFIG on their own
even though the environment variable was already exported.

Link to hackint.org added

The u-boot package has some issues causing its build to fail under certain
circumstances. As we don't support the ZyXEL devices it's used for anyways, just
don't build it anymore.