Add setting to exclude certain regex patterns of urls and local file paths

[alexweininger]

It would be awesome to be able to exclude certain PDFs from the list based on either their URL or the local file path they were stored in.

Maybe also being able to exclude PDFs based on regex patterns matching the names of the files.

[sharath2106]

@alexweininger I'd like to work on this. Do you have any ideas in hand now? I'm thinking of adding an option in the settings page.