Add Classs Metaddata() for metadata CRUD

[LinkunGao]

Description:

Describe what changes you are adding

• finished editing dataset_description metadata:
  • add_values with multiple value args or *[value1, value2,...]
  • get_values
  • remove_values

    Related issue(s):

    87

Test Environment:

Specify the testing enviroment. e.g. OS, Python version

[LinkunGao]

dataset_description.clear_values() has two use modes:

1. use dataset_description.clear_values() with no params:
   • This will remove all field values, and go back to the default Excel file.
2. use dataset_description.clear_values(field_name='Contributor role') with field_name param:
   • This will remove all values in Contributor role element