Feature/assetvalidation (#3396)

# To run the script
Make sure to install the latest Python API version `openspace-api 0.1.2`
The script is located in `OpenSpace/support/assetvalidation`, the main script takes a few command line arguments

`--dir` - specify the OpenSpace directory 
`--filter` - optionally supply a regex string to filter which assets to validate
`--verbose` - flag to print debug info to log and also console (default off), if off only warnings and errors are logged
`--start` - flag to start OpenSpace as a subprocess (default on) if this is off it assumes OpenSpace is already running, useful if you want to run OpenSpace via Visual Studio for example. 
`--at` - specify an index to start at a specific asset

run eg: 
`python main.py --dir="C:/User/Desktop/OpenSpace" --filter="examples" --verbose=True --start=False --at=35`

include/openspace/rendering/dashboard.h

@@ -52,6 +52,7 @@ public:
     void removeDashboardItem(int index);
     void clearDashboardItems();
     glm::vec2 getStartPositionOffset();
+    std::vector<DashboardItem*> dashboardItems() const;
 
     /**
      * Returns the Lua library that contains all Lua functions available to affect the