CRUD optimizations for qna sections

[feich-ms]

Optimize CRUD operations for qna sections which will be consumed by composer qna editor.

[liweitian]

Found some problems on it. Need to discuss with @feich-ms . Do not merge it at this time.

[codecov-commenter]

Codecov Report

Merging #854 into master will decrease coverage by 0.69%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #854      +/-   ##
==========================================
- Coverage   58.01%   57.31%   -0.70%     
==========================================
  Files         214      214              
  Lines       15368    14972     -396     
  Branches     2055     2078      +23     
==========================================
- Hits         8915     8581     -334     
+ Misses       5908     5830      -78     
- Partials      545      561      +16     

Impacted Files	Coverage Δ
packages/lu/src/parser/lufile/luParser.js	89.51% <75.00%> (-1.77%)	⬇️
packages/lu/src/parser/lufile/qnaSection.js	89.47% <75.00%> (-1.12%)	⬇️
packages/lu/src/parser/lufile/sectionOperator.js	90.00% <83.33%> (+1.42%)	⬆️
packages/lu/src/parser/cross-train/crossTrainer.js	94.71% <100.00%> (+2.40%)	⬆️
packages/lu/src/parser/lufile/parseFileContents.js	80.54% <100.00%> (-1.07%)	⬇️
...mathematics/confusion_matrix/AppConfusionMatrix.ts	6.66% <0.00%> (-22.32%)	⬇️
...kages/luis/src/commands/luis/application/create.ts	61.11% <0.00%> (-19.85%)	⬇️
...rc/commands/luis/application/assignazureaccount.ts	82.60% <0.00%> (-17.40%)	⬇️
...ackages/luis/src/commands/luis/application/list.ts	84.61% <0.00%> (-15.39%)	⬇️
...ckages/luis/src/commands/luis/application/query.ts	73.33% <0.00%> (-14.17%)	⬇️
... and 84 more

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