Test refactor dqc wrapper

See merge request ces/c3s512-wp1-datachecker!11

# Conflicts:
#   dqc_wrapper/checker.py
#   dqc_wrapper/test00_file_format.py
#   dqc_wrapper/test01_standard_compliance.py
#   dqc_wrapper/test02_spatial_completeness.py
#   dqc_wrapper/test03_temporal_completeness.py
#   dqc_wrapper/test04_spatial_consistency.py
#   dqc_wrapper/test05_temporal_consistency.py
#   dqc_wrapper/test06_valid_ranges.py

Refactor code

* Read timestamps from cd3-forms (for temporal completeness)
* Specify a file pattern + Input directory
* Deleted unnecessary code and folders
* Refactoring and formatting of code
* Comments and description of classes
* Moved to CDO bindings for test04 and test05
* Command-Line parameters moved to a more user friendly and powerful configuration file system
* Created several tests for each of the checks (each one as a separate configuration file)
* Centralized log file creation and directory reading to utils_files.py
* Updated documentation and README
* Finished up test04 and test05

See merge request ces/c3s512-wp1-datachecker!10

Merge branch 'refactor_code' of https://earth.bsc.es/gitlab/ces/c3s512-wp1-datachecker into refactor_code

# Conflicts:
#	dqc_wrapper/checker.py
#	dqc_wrapper/test00_file_format.py
#	dqc_wrapper/test01_standard_compliance.py
#	dqc_wrapper/test02_spatial_completeness.py
#	dqc_wrapper/test05_temporal_consistency.py
#	dqc_wrapper/test06_valid_ranges.py

Long list of modifications after testing code on real data: allow single files, correct netcdf2 issue, add spatial_consistency test,...