prores.py: add logo option

same adding a logo argument as in bitc.
this is for a discrete logo to be added to top right hand corner
in the bitc script it is: ('overlay=main_w-overlay_w-5:5')

the logo png is stored (for ease of purpose) in the ifigit/ifiscripts folders on es1 & 2 and macmini. if you need it for testing: ifi_logo_small.png

R