Fixes for SQ type and unit tests, squashed from PR 64

[smjoshiatglobus]

I got entangled in Git mess! Here are the same changes, as one squashed commit:

Main changes:

• Added support for elements of type SQ for unit tests. This has fixed some failing unit tests and I managed to remove several test files from the exclusion list.
• Fixed anonymization failures for RawDataElement type of elements, which are NamedTuple, issue Tag replacement fails during anonymization for structured reports #63
• Changed anonymized value for CS and some other types to all uppercase 'ANONYMIZED'. The CS VR type required uppercase characters per https://dicom.nema.org/medical/dicom/current/output/html/part05.html#table_6.2-1
• Now the number of passing tests have increased from 313 to 397.

Other changes, mostly for development support:

• Added references to known issue X tags of VR == 'DA' not getting deleted #56 in tests code
• Added Pipfile for optional development setup using pipenv
• Added configuration for spell-checking using cspell and added custom dictionary.
• Fixed a typo (only one!)
• Formatted code in tests and example folders using black
• Suppressed some warnings from Sourcery

[pchoisel]

LGTM
Thanks for taking the time !
The PR is marked as draft, but can I merge it ?

[smjoshiatglobus]

LGTM Thanks for taking the time ! The PR is marked as draft, but can I merge it ?

Yes! I have marked it ready now. It is a regular pull request now.