Fixes #414

While ath9k/ath10k devices can supprt VIFs with any combination of MAC addresses, there are also adapters which have a hardware MAC filter which only allows a few bits to differ. This commit changes the addresses of all VIFs to ony differ in the last 3 bits, which is required to support many Ralink/Mediatek based WLAN adapters.

Technically, the new addresses are generated by calculating an MD5 hash of the primary MAC address and using a part of this hash as a prefix for the MAC addresses.

The addresses (BSSIDs) of the AP VIFs are also reused for the LAN and WAN interfaces in mesh-on-LAN/WAN mode to reduce the number of needed addresses, and thus reduce the chance of collisions. This is not a problem as the MAC addresses of the AP VIFs are never used except as BSSID, and thus not seen by routing protocols like batman-adv.

Fixes #648

[Matthias Schiffer: rewrote commit message]

gluon-announced and gluon-announce are merged to gluon-respondd.

This will allow us to use its content from other languages than Lua as
well.

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

The now empty gluon-firewall is removed.

This is the most basic core of the Gluon framework. Most upgrade scripts will
have to be rewritten and/or moved to other packages.