Allow _RenderPassNameWidget UI to remain open when adding multiple passes

[nikos3d]

Summary

We would like the _RenderPassNameWidget UI (accessed via the RPE + button) to remain open when adding multiple passes.

User story

In a production environment it is common to create multiple passes at once and it would therefore help if the UI could remain open while the passes are being created.

What

Example workflow:

1. Press + in the RPE to add new pass(es)
2. Press "Add" to create pass A (the UI remains open)
3. Press "Add" again to create pass B (the UI still remains open)
4. Press "Add" to create the last pass C (it's still open...)
5. Press "Cancel", when done, to close the UI.

Why

This would speed up the general workflow as you wouldn't have to hit the plus + button each time you want to add a new pass.

Feature proposal

The Widget UI currently consists of two buttons, "Cancel" and "Add". The idea is simple: Don't close the UI when "Add" is pressed. Only allow for closure with the "Cancel" button, which might require re-labelling to something like "Close".