Modify how modulo is calculated in Normal and Scientific mode. (#412)

## Fixes #111

> The modulo operator on this calculator gives the result that is different to the most used calculators.

The current `modrate` function is the equivalent of rem(...)/remainder(...), not mod(...)/modulo(...) available in some popular Math apps. 

### Description of the changes:
- rename `modrate` in `remrate` to be more accurate.
- add `modrate`, calculating modulo similarly to Matlab, Bing, Google calculator, Maxima, Wolfram Alpha and Microsoft Excel 
- Add `RationalMath::Mod` using `modrate` as an alternative to `Rational::operator%` using `remrate`
- Add a helper `SIGN` to retrieve the sign of a `Rational`.
- modify `CalcEngine` to use `modrate` in Normal and Scientific mode and `remrate` in Programmer mode.

### How changes were validated:
- manually and unit tests added

src/CalcManager/Header Files/CalcEngine.h

@@ -45,7 +45,7 @@ namespace CalculationManager
     class IResourceProvider;
 }
 
-namespace CalculatorUnitTests
+namespace CalculatorEngineTests
 {
     class CalcEngineTests;
 }
@@ -160,5 +160,5 @@ private:
     static void ChangeBaseConstants(uint32_t radix, int maxIntDigits, int32_t precision);
     void BaseOrPrecisionChanged();
 
-    friend class CalculatorUnitTests::CalcEngineTests;
+    friend class CalculatorEngineTests::CalcEngineTests;
 };

src/CalcManager/Header Files/RationalMath.h

@@ -13,6 +13,7 @@ namespace CalcEngine::RationalMath
     Rational Pow(Rational const& base, Rational const& pow);
     Rational Root(Rational const& base, Rational const& root);
     Rational Fact(Rational const& rat);
+    Rational Mod(Rational const& a, Rational const& b);
 
     Rational Exp(Rational const& rat);
     Rational Log(Rational const& rat);