[New feature] Expose 'generate sortspec' function(s) to simplify onboarding process

[SebastianMC]

To simplify the initial set up of the plugin expose one or more features from the list below:

• in settings, a set of buttons to generate the initial sortspec note(s) with sorting spec skeleton or an example sortspec or with a list of top-level folders, or similar
• context menu on folders, which would generate the sortspec for that folder, containing the list of files in the folder
• more ideas to come