Reduce necessary valid signatures for stable updates to two down from three
Remove probability field from update branches, as it was retired in 2014.3
Bump to 0.5.2

Based on Gluon 2014.3.1, OpenWRT 12.07 (Attitude Adjustment)
- alfred: backport from master branch
- config-mode: Setting an SSH password in config mode will not remove public keys anymore
- config-mode: The "Fertig"-Button in the Wizard was renamed to "Speichern & Neustarten" to better reflect its behaviour
- gluon-wan-dnsmasq: allow configuring static DNS servers
- gluon-mesh-vpn-fastd: delete all old backbone peers on update
- gluon-luci-portconfig: expose advanced WAN configuration