Add htcondor submission

This MR adds HTCondor processing helper scripts to salt.

It makes use of a helper class to dynamically create the submission files for HTCondor.

Also it adds a bash convenience script to launch the salt container from unpacked at cvmfs.

• implement decent class member variables for the HTCondor submission
• add an option to schedule singularity in HTCondor jobs to allow without local conda setup
• add documentation