Trekstore Surftab Wintron 7.0 III: Linux

See post about hardware: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-hardware.html
See post about UEFI: https://technikgebastel.blogspot.de/2016/03/trekstore-surftab-wintron-70-i-uefi.html
See post about Linux: https://technikgebastel.blogspot.de/2016/04/trekstore-surftab-wintron-70-iii-linux.html

Current status:

What works (tested):
- booting Debian or Ubuntu with XFCE4, i3, Gnome3
- display: brightness change, screen rotation, video playback
- touchscreen (GSL1686): calibration, multitouch input (including multitouch gestures in Gnome3)
- Wireless (rtl8723bs)
- USB-OTG
- micro-SD card slot
- battery charge state (AXP288)

- orientation sensor (bma22e with BMA2x2)

What probably works (not tested):
- Bluetooth (rtl8723bs)

What does not yet work:
- audio output (ALC5651 not supported with linux kernel 4.3, included starting 4.5, but wlan-patches for 4.5 cause problems)
- cameras (gc0310, ov2680)

What will probably never work, aka no idea how to make it work:
- hardware buttons (except power button)

Once everything except stuff in the category "What will probably never work, aka no idea how to make it work:" is working, I will document everything here.