Remove class objects from DataStore

[mylibrar]

This PR fixes #898 .

Description of changes

• Refactor FNdArray and add conversion layer to entry_getter and entry_setter in BasePack.on_entry_creation.
• Remove deprecated image_annotations in DataPack.
• Remove redundant __getstate__ and __setstate__ methods in Annotation and AudioAnnotation.
• Serialize Span in replace_back_operations and processed_original_spans from Payload to make it JSON serializable.
• Revert get_parent and get_child in MultiPackLink

Test Conducted

• ndarray_attribute_test.py (test FNdArray conversion)
• html_reader_test.py (test Span conversion)

[codecov]

Codecov Report

Merging #899 (8f8c319) into master (3ba5d8f) will increase coverage by 0.15%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master     #899      +/-   ##
==========================================
+ Coverage   80.85%   81.00%   +0.15%     
==========================================
  Files         254      254              
  Lines       19607    19583      -24     
==========================================
+ Hits        15854    15864      +10     
+ Misses       3753     3719      -34     

Impacted Files	Coverage Δ
forte/data/data_pack.py	85.07% <ø> (-0.03%)	⬇️
forte/data/base_pack.py	76.68% <85.71%> (+0.51%)	⬆️
forte/data/data_store.py	93.25% <100.00%> (+0.01%)	⬆️
forte/data/ontology/core.py	82.47% <100.00%> (+5.51%)	⬆️
forte/data/ontology/top.py	78.74% <100.00%> (+3.05%)	⬆️
forte/data/span.py	82.75% <100.00%> (+3.59%)	⬆️

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