Unclear default preprocessor order for time related preprocessor functions

[bouweandela]

It looks like there has been a mistake when fixing a merge conflict in #696 and now the default order in which the preprocessor functions are applied is no longer clear because several preprocessor functions are mentioned twice in the list that defines the order:

ESMValCore/esmvalcore/preprocessor/__init__.py

Lines 90 to 104 in 1c9885b

	# Extract years given by dataset keys (start_year and end_year)
	'clip_start_end_year',
	# Time extraction
	'extract_time',
	'extract_season',
	'extract_month',
	'resample_hours',
	'resample_time',
	# Data reformatting/CMORization
	'fix_data',
	'cmor_check_data',
	# Time extraction (as defined in the preprocessor section)
	'extract_time',
	'extract_season',
	'extract_month',

I think that all time related preprocessor functions would need to be moved after cmor_check_data, but can you please check @schlunma and @jvegasbsc?

[schlunma]

Yes, all non-default preprocessors that can be specified by the user in the recipe should be moved after cmor_check_data so that custom_order: true works with them (see #762). Thus, the order should be:

    ...
    # Concatenate all cubes in one
    'concatenate',
    'cmor_check_metadata',
    # Extract years given by dataset keys (start_year and end_year)
    'clip_start_end_year',
    # Data reformatting/CMORization
    'fix_data',
    'cmor_check_data',
    # Time extraction (as defined in the preprocessor section)
    'extract_time',
    'extract_season',
    'extract_month',
    'resample_hours',
    'resample_time',
    # Level extraction
    'extract_levels',
    # Weighting
    'weighting_landsea_fraction',
    ...