Improve model deserialization

[eduardomourar]

Issue #, if available: #9

Description of changes:
This improves the deserialization of the raw model into the proper classes.

• ser/de can now handle complex schemas containing arrays and objects (related to Data class with model validation #1)
• CloudFormation service is casting all primitive types (integer, number, boolean) into strings. This provides a hacky, but easy-to-remove-once-fixed-upstream, convertor that re-casts them back to their intended types.

[codecov]

Codecov Report

Merging #18 into master will increase coverage by 3.01%.
The diff coverage is 99.55%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
+ Coverage   94.45%   97.47%   +3.01%     
==========================================
  Files          11       13       +2     
  Lines         793      870      +77     
  Branches      118      148      +30     
==========================================
+ Hits          749      848      +99     
+ Misses         44       22      -22     

Flag	Coverage Δ
#unittests	97.47% <99.55%> (+3.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/rpdk/typescript/utils.py	100.00% <ø> (ø)
src/utils.ts	100.00% <ø> (+16.94%)	⬆️
src/proxy.ts	96.49% <97.14%> (+16.13%)	⬆️
python/rpdk/typescript/codegen.py	100.00% <100.00%> (ø)
python/rpdk/typescript/resolver.py	100.00% <100.00%> (ø)
src/index.ts	100.00% <100.00%> (ø)
src/interface.ts	100.00% <100.00%> (+3.77%)	⬆️
src/log-delivery.ts	93.25% <100.00%> (ø)
src/metrics.ts	100.00% <100.00%> (ø)
src/recast.ts	100.00% <100.00%> (ø)
... and 3 more

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