Add case-insensitive matching for flow names

[fjuniorr]

Closes #46

• add FlowProperty class to handle storage of original and normalized versions of flow properties
• strip falsy elements from list in FlowProperty.normalize

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (8ba9347) 74.61% compared to head (14e26d5) 77.06%.

Files	Patch %	Lines
flowmapper/flowproperty.py	97.72%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #57 +/- ## ========================================== + Coverage 74.61% 77.06% +2.44% ========================================== Files 11 12 +1 Lines 390 436 +46 ========================================== + Hits 291 336 +45 - Misses 99 100 +1 ```

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