Added support for unit of measurement

[gbenziv]

Closes #194

• Created UOM entity
• Updated API comments
• Added UOM to stack DB
• Added validator and display
• Added unit tests

Pull Request Checklist

• [x] I have ensured that my commit message contains the Issue ID.
• [x] I have ensured that my commit message contains the feature/bugfix description.
• [ ] I have updated the documentation accordingly.
• [x] I have ensured my code follows the coding guidelines.
• [x] I have ran lint in my code locally prior to submission.
• [x] I have built my changes in local successfully.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov[bot]]

Codecov Report

Merging #195 (1c1f69a) into master (ed97599) will increase coverage by 0.12%. The diff coverage is 95.55%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
+ Coverage   95.33%   95.45%   +0.12%     
==========================================
  Files          45       46       +1     
  Lines         900     1034     +134     
==========================================
+ Hits          858      987     +129     
- Misses         42       47       +5     

Impacted Files	Coverage Δ
core/domain/common/basecontroller.hpp	100.00% <ø> (ø)
core/domain/common/cachecontroller.hpp	100.00% <ø> (ø)
core/domain/inventory/inventorycontroller.hpp	100.00% <ø> (ø)
core/validator/productvalidator.hpp	100.00% <ø> (ø)
core/domain/unittest/test_inventory.cpp	96.66% <93.18%> (-3.34%)	:arrow_down:
core/domain/inventory/inventorycontroller.cpp	97.82% <100.00%> (+2.91%)	:arrow_up:
...main/unittest/mock/inventory/inventorydatamock.hpp	100.00% <100.00%> (ø)
core/entity/uom.hpp	100.00% <100.00%> (ø)

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