five star rating of pictures

How I do it now
Assume having a folder containing the pictures of an event/vacation/etc. I usually create a subfolder "best-of" or similar containing a subset with the best pictures. This leads to duplicates of pictures and is kind of a messy way to organize photos.

Describe the solution you'd like
I would like to suggest a rating system for Photos. Every user could develop his own rules. Mine would be for example

• 1*: default
• 3*: best 20 pics
• 4*: best 5 pics
• 5*: absolute masterpiece, maybe 20 pictures in all of my photos.

In order to do this, following features are needed:

• initially, all pictures are unrated
• bulk rating per album/folder should be possible (eg. set all to ***..)
• Set rating directly when viewing them, therefore the viewer would need to feature a rating element.
• When viewing an album/folder, one should be able to filter e.g. tree stars and above
• Cherry on top: when sharing an album, only share 3 stars or better

Describe alternatives you've considered
Folder with a subset copy of the best 20 something pictures.
At the moment there is a star feature in Photos. This doesn't allow for a more defined rating, plus you cant filter albums by starred pictures, only a global view of them.

No files, tests, or entry points are named in the issue. Review merged pull request #3491 first to determine what remains; done would require the requested rating, bulk assignment, filtering, viewer control, and sharing behavior.