Fixing a few configuration bugs

[hunterhector]

This PR fixes #542

Description of changes

1. Allow caster to assign a name to multipack automatically
2. When creating new data pack in multi packs, allow assigning a name
3. Add clear exception when constraint_type is not set in ontology code generator
4. Do not query selector_config when it is None.
5. Remove unused function new_data_pack in pack_processor
6. Check for output_dir in writers.

Possible influences of this PR.

Describe what are the possible side-effects of the code change.

Test Conducted

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[codecov]

Codecov Report

Merging #541 (4648f2e) into master (9170f30) will decrease coverage by 0.00%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master     #541      +/-   ##
==========================================
- Coverage   79.59%   79.58%   -0.01%     
==========================================
  Files         222      222              
  Lines       15914    15917       +3     
==========================================
+ Hits        12667    12668       +1     
- Misses       3247     3249       +2     

Impacted Files	Coverage Δ
forte/processors/base/pack_processor.py	86.66% <ø> (+3.33%)	⬆️
forte/processors/base/writers.py	68.60% <33.33%> (-1.28%)	⬇️
forte/data/ontology/ontology_code_generator.py	89.71% <50.00%> (-0.20%)	⬇️
forte/data/caster.py	95.23% <100.00%> (+0.23%)	⬆️
forte/data/multi_pack.py	78.11% <100.00%> (ø)
forte/pipeline.py	93.53% <100.00%> (ø)

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