Add a pinboard/favourites list

[NickGeek]

Is your feature request related to a problem? Please describe.
I have a number of notes I like to keep track of but don't have due dates.

Describe the solution you'd like
I'd like a list similar to the "Upcoming due dates" one with a list of pinned/starred notes. There should be an easy way to pin/star a note (maybe on the breadcrumbs near the date)

Describe alternatives you've considered
Global search does the job for now. You could also just use a #pin or #fav hashtag to do it.