Made Revit geometry conversion functions public for use in Python scripts

Fix for user reported issue: https://github.com/tt-acm/EnergyAnalysisForDynamo/issues/76

This is another one of those issues arising from: https://github.com/DynamoDS/Dynamo/pull/2892/

These API's are used by end-user python scripts and have been made public:
```
RevitToProtoMesh
RevitToProtoFace
RevitToProtoSolid
RevitToProtoCurve
GeometryObjectConverter
```

@ikeough @pboyer @kronz please review these changes