Search for entries with no tags or stars with -not -starred and -not -tagged - #1663

This aims to fix #1057 - Filter for entries with no tags

As discussed in that issue, the preferred syntax is -not -starred & -not -tagged, as this feels the most intuitive

I aimed to change the existing functionality as little as possible, but making this syntax fit did necessitate some minor changes:

• Add a -tagged flag, to show only tagged entries
• Alter -not to be allowed to take 0-1 arguments
• Manage parsing in case proceeded by -starred or -tagged
• If not is not followed by either tag, and is empty, then return the error we would normally get

Note: While I agree that -not -starred etc is the most intuitive syntax (it's what I instinctively tried initially), I'm not crazy about the double usage for the -not flag. Ideally each flag should only do one thing, but if we want to go a different route I can take a look at that also :-)

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.