Add implementation of CVI - Chaikin's Volatility class and related tests.
* **Cvi Class Implementation:**
- Add `Cvi` class in `lib/volatility/Cvi.cs` to calculate Chaikin's Volatility.
- Use high and low prices for calculation.
- Include a constructor with `period` parameter.
- Add a method to calculate Chaikin's Volatility.
* **Quantower Indicator:**
- Add `CviIndicator` class in `quantower/Volatility/CviIndicator.cs`.
- Use `Cvi` class for calculation.
- Add input parameters for `period` and `showColdValues`.
- Implement `OnInit` and `OnUpdate` methods.
* **Tests:**
- Add a test method for `Cvi` class in `Tests/test_updates_volatility.cs`.
- Use random updates to test `Cvi`.
- Ensure initial and final values are equal.
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Miha Kralj