fix finding of pad neighbours; remove methods to write them in OCDB

fix finding of pad neighbours; remove methods to write them in OCDB

Round slates are rotated compared to others so the pad density
increases instead of decreasing when going from left to right:
--> increased number of possible neighbours from 10 to 12 to be
full symmetric (also consider increasing density from bottom to top)
--> corrected possibility to store the neighbours at their
corresponding position in the array (holes filled with invalid pads)