Rework of file handling to object-oriented approach

The whole (input) file handling mechanism was reworked to use an object-oriented approach. Following this, most of the scripts (prepare_member, remapping, samoa and validation) are rewritten in Python to make use of it. A few other internals were changed:

• Python utils are now stored in a separate directory (in LOGDIR).
• There is a workflow directory (in LOGDIR) storing information on used domains and files (as a list of Python objects).
• Added a job to remap ERA5 data to the ICON grid (Levante only).
• Removed bash_utils.sh (obsolete).
• Renaming: process_grid_info -> icon_file_handler.
• Separate job added to collect all input files in the beginning.
• Added job to clean up remote before execution (for testcases).
• Added switches for turning pipelines on and off for Horeka and Levante.
• Added an experiment config python module.
• Did a major cleanup.

Fixes #113 (closed). Closes #51 (closed), #116 (closed), #126 (closed).