New feature: Install modules by drag-and-drop Python files

Until now, if developers wanted to add custom modules to Slicer, they had to open application settings, go to developer section, and append folders to the module list there.

Now there is a simpler way to install modules: just drag-and-drop the .py file (or parent folder) to the Slicer application screen and click OK to “Add Python scripted modules to the application”.

Then you are offered an option to select certain modules or add all the modules that are found in the folder. Modules are immediately loaded and ready to use - no need to restart Slicer (only if the module performs initializations at application startup).

The feature is available in latest Slicer Preview Release (Slicer-5.3 rev 31632 and later). Any comments and suggestions are welcome.