Create pngs of raw and calexp (or postISRCCD) images for obslog

We are going to start deleting processed data on the summit, which means that calexps will not be available after a week or so. Currently, obslog uses the calexps to make the png files which it displays (but only makes them on-demand).

Please modify the drp pipelines to create the pngs of both the raw and a processed file (calexp or postISRCCD). We'll have to make sure that they aren't purged with the FITS files.

michitaro tells me that he creates pngs with maximum width and height of 150, 300, and 600 pixels so we'll need all three sets of files.