Add new options to assets item context menu

Currently we can access context menu by right-clicking an asset in assets library and only delete option is available.
It would be beneficial and useful to be able to:
-open the selected file in explorer/file browser;
-add "open" button that allows to open an image with existing qtc/qds image viewer (however this one will probably drop user out of design mode);
-probably will be harder to implement, but other useful options from qtc file & project views, like rename asset with rename of all asset usage and search of usage.