Address reviews

- Adding new `CompositeAlphaModel.AddAlphaModel()`
- Adding C#/Py regression algorithms using the new `QCAlgorith.AddAlphaModel()`
- Improving exception message
- Add python version of `QCAlgorith.AddAlphaModel()`

Algorithm.Python/QuantConnect.Algorithm.Python.csproj

@@ -36,6 +36,7 @@
     <LangVersion>6</LangVersion>
   </PropertyGroup>
   <ItemGroup>
+    <Content Include="AddAlphaModelAlgorithm.py" />
     <Content Include="Alphas\ContingentClaimsAnalysisDefaultPredictionAlpha.py" />
     <Content Include="Alphas\ForexCalendarAlpha.py" />
     <Content Include="Alphas\GasAndCrudeOilEnergyCorrelationAlpha.py" />
@@ -252,4 +253,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>