Changed order of variable renaming at send_file to avoid errors. Better management of valid_min and valid_max attributes

Merge branch 'v3.0.0b1_bug_fix_ohc' of https://earth.bsc.es/gitlab/es/ocean_diagnostics into develop-python_migration

Created a class to encapsulate al the experiment management (get chunk list, get member str...) functionalities

Minor changes to make the diagnostics more user-friendly. Removed old diagnostics. Added measurement of time consumed by each diagnostic class