Double click on a node or an attribute with an image file to display it in the 2D viewer.
Contextual menu to expose additional actions: * open media containing folder * copy media path * advanced manual control over media (un)loading + fix MediaLibrary to avoid binding loop on 'visible' when directly modifying 'request' property
For python 2 / 3 compatibility
* avoid non-cross platform hacks to convert string path to urls * use standard python API
