Generate flashable images for the Archer C7 v2 with current stock firmware
again.

To set the region code, the GLUON_REGION variable must be set to "us" or
"eu" in site.mk or as a make argument.

Fixes #860

and add documentation

Fixes #823

Newer versions of Sphinx would break lines at the colons.

link to site-repo updated

Change the limit to match our recommendation in the site-example.

Also
* create list of newly supported devices since v2015.1.2 in the v2015.2 release notes
* update information on docs/user/x86
* fix a comment in targets/ar71xx-generic/profiles.mk

This commit basically does two things: it urges users always to use an own
git repository to manage the site configuration, and it removed all
mentions of "communities" from the "Getting started" page, as it was too
Freifunk-specific.

Other documentation pages (especially the site configuration docs) should
probably be adjusted as well.

The Freifunk Münsterland firmware was formerly known as Freifunk Münster firmware - while the URL hasn't changed. In future, there will probably be subdomains with their own files, but for now this is state of the project.

`make modules` will generate a opkg repository containing kernel modules
matching the kernel of the Gluon images.

We'll soon have other output besides the images, having a single directory
for all output makes sense.

Fixes #487

gluon-radio-config contained only a single file. The code has been adjusted
to allow creating a Gluon configuration without WLAN support by removing
the wifi24 and wifi5 sections from site.conf.

The Gluon-specific functions of the gluon-simple-tc package are moved to
gluon-mesh-vpn-fastd.

The new options allow specifying custom repositories and are evaluated
in an upgrade script, not during build.

Fixes #401