Distribute buttons of equal size
[pixelpos,normpos]=lm_distribute(LM,RM,TM,N)
LM: left margin (pixels)
RM: right margin (pixels)
TM: margin in between (pixels)
N: number of objects to distribute
pixelpos(N,4): input argument prepared for lm_linkobj
normpos(N,4) : input argument prepared for lm_linkobj