Maya: AssetManager: 1. Added TimedExportProcess class to asset_manager_alembic_functionality to catch crashed export jobs. Time limit setting per UI tbd. 2. Refactored export method in asset_manager and added checks for props. 3. Updated context menu for props metadata to show and hide proxy, rendergeo and locator objects in the scene. Visibility became a function and is not an attribute anymore. (That did not make sense anyway since it was weak and would have never been correct). 4. Removed visibility from all prop MVC classes. HelgaAssetMetadata plugin: 1. Removed visibility as an node attribute on HelgaPropMetadata and HelgaCharacterMetadata.