0.5.7: Fix disabled geometry pathpoint editor popup

0.5.7 is purely a bugfix release. The main fix is that the GeometryPath editor popup has now returned. It dissapeared because opensim-core now supports function-based muscle paths.

• Fixed PathSpring components ignoring the scene scale factor (#816)
• Fixed a bug where the property editor for a muscle's geometry path was not rendering the customized muscle path point editor popup (#815)
• Fixed PathSpring not using it's GeometryPath's color correctly in OpenSim (#818, upstream: opensim-core/#3668)
• Internal: ImGui now renders its content via the oscar graphics API, rather than via its own internal OpenGL backend
• Internal: oscar pure-virtual interface classes are now prefixed with I (e.g. ITab, IPanel, etc.)
• Internal: OpenSimCreator pure-virtual interface classes are now prefixed with I (e.g. IOutputExtractor, ISimulation, etc.)