update devices (#83)
update devices (#83)

* add Asus RT-AC51U
* add new image name for GL.iNet GL-AR150/GL-AR300M/GL-AR750
* add GL.iNet GL-MT300n v2
* add Mikrotik nand AC/nor 16m/nor 16m AC
* add Netgear R6120
* add WT3020(AD/F/H)
freifunk-darmstadt/gluon-firmware-wizard,codedust/gluon-firmware-wizard,freifunk-darmstadt/gluon-firmware-wizard,codedust/gluon-firmware-wizard,freifunk-darmstadt/gluon-firmware-wizard,codedust/gluon-firmware-wizard