GUI Support for "Pin" and "Favorite" tagging of apps, in Application Settings pane for each VM

[ninavizz]

This is a child issue within the epic #6665

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The problem you're addressing (if any)
For #5677 we created a host of new features to eventually roll-out in the app menu. Among the most popular, were enabling folks to keep a "Favorites" menu, and to "pin" apps to the top of their sub-menu for each qube.

Describe the solution you'd like

1. The most sensible place in the GUI to enable users to act upon these features, is in the VM Settings: Application Tab.
2. I would also like to see both of these features included in the Right-Click menu for apps, in each qube's sub-menu.

For #6366 I pitched this redesign, that can elegantly extend to support the two GUI features this Issue was created to track.

Where is the value to a user, and who might that user be?
Users can, today, mark an app a Favorite, on the command line. This is regrettably not even discoverable to many technical users. For both technical and non-technical users, it will make the ability to customize one's app menu for the most efficient per-user use, a breeze—which will make Qubes a more overall useful and pleasant OS to use on a regular basis.

Describe alternatives you've considered
Keeping it all on the command-line. Which would be a drag.

Related, non-duplicate issues
#6366

[valereznya]

It is delightful and most wonderful that you are bringing color and joy into QubesOS. We were playing in the morning and last night adding optional features for VM Creation in the PyQt GUI of "Create Qubes VM" Dialoge found in the XFCE menu -- disk encryption, optional ramdisk/memory encryption and (greyed out) something else. We would have so much enjoyed to consult with you, rather than deciding ourselves whether the label should be placed above "Provides network" (Disk Encryption, checkbox too), or below it, have a (colorful!) icon or a special font, or should be sorted into Qubes Settings / Advanced. Please keep up the spirit to make privacy and encryption more of a colorfully thoughtfully designed adventure, wired and colorfully sorted like Ethernet cables in a rackmount, rather than a vintage computer museum of grey and techniques. Of course XEN and Security leading to Privacy is very technical, but like vi syntax highlighting colors enshining on code matter.