add --finished and --started flag to list subcommand

**Is your feature request related to a problem? Please describe.**
Sometimes I am not interested in the whole library content but only in the books I am currently reading or already read. This should be an option to filter for.

**Describe the solution you'd like**
Adding a flag `--finished` and `--reading` to the `list` subcommand could solve this.

**Describe alternatives you've considered**
A workaround would be to add the books to different shelfs. Filtering for this is already working, but because of the missing possibility to edit an existing book, this is not acceptable.