rename varibles in  _check_filters (observations.py) to reflect that  properties are also included, fixes documentation

Modify ObservationsManagerPassbands to iterate over an instance of observationclass,  modify Workers accordingly and to include the properties and modify pdf_anaysis/utils to include properties in compute_chi2, _cimpute_scaling and dchi2_over_ds2

Include properties in _check_filters, _check_errors, _check_invalid (only extensive) and add_model_error functions in observations.py. rename errors as bands_errors

Add ParameterManager as input to ObserbationsManagerPassbands class, this is use to separate the intensive properties to fit from the extensive and add them to the class. Modify pdf_analysis/__init__.py to call ParameterManager befor ObservationsManager

modify models.py to use get_info from utils, add intprops and extprops property to ModelsManager class

When using different line widths during a single run, ensure that the fluxes and other quantities are always computed correctly

Ensure that the computation of the continuum level is correct when determining the equivalent width, in particular when the line width is very narrow.