Docs

• Added Modal module documentation.
• Added Asset model documentation.
• Improved Modal API documentation.
• Improved Assets module documentation.

Added

• Support custom Modal with the new config.modal.custom option.
  More about this here.
• Added modal catch-all event to Modal module.
• Support custom AssetManager with the new config.assetManager.custom option.
  More about this here.
• Added open and close methods to AssetManager.
• Added getType and getSrc methods to Asset class.

Fixed

• Fixed rendering issue with custom traits #3735