[feature] Add user account support with "parent/child" tab groupings

**Version and OS**
0.39.12 on linux/docker

**Is your feature request related to a problem? Please describe.**
No.

**Describe the solution you'd like**
It would be nice to have completely different users without actually making two containers running to save resources. Let's say your partner wants to use the tool as well. For now, we can use tags as the solution to separate in tabs different themes if you will. However, let's say you want to separate work from home, your wife's things from yours, so naturally you would want different **defaults** (which e-mail to notify, check times, etc).

See the example in the print


By the way, what an excellent tool! keep up with the good work!

No files, tests, or entry points are named. Start by mapping the existing tag/tab grouping and notification/default-settings flows; completion would require a defined account model that separates users and their defaults, but the issue does not specify authentication or acceptance criteria.

Written by the indexing model from the issue text.