removed all the hardcoded symlinks to full pleiades images.

Now each stereo dataset contains one or two text files containing the
relative paths to the panchro and/or multispectral images. The symlinks
have to be generated by the user using the script 'create_links.sh'
located in the 'pleiades_data' folder.
add shell script to generate the symlinks to the pleiades data
cleanup
added rpc data for all the available pleiades datasets