New setup and streamlined task structure to reflect first round of feedback

Things left to do:

• Configurable setup variables
• Move command execution back to tasks, provide helper in base class
• Move plotting to external functions, just use them from within law tasks
• Linearize tasks structure somewhat more
• Document all functions (e.g. in utils)
• Make some features more functional (e.g. plot viewing)
• Use code checkout for condor jobs instead of "getenv"
• Move HH model file to more prominent location, currently hidden in dhi/utils
• Revise documentation once all the changes above are implemented
• Update HH model
• Add working gfal2 bindings for remote file access