Better error messaging when something goes wrong messaging members

[danamlewis]

I ran into multiple PEBCAK errors messaging members of a project recently, so I'd love to return a better error message to help project admins troubleshoot! Right now, if you goof up in any of the following ways, the message returned is the same: "a comma separated list of project member IDs".

I would suggest these scenarios to have better messages returned:

• Duplicate member IDs in the list.
  • (Warn about duplicates; or still process the request ;))
• 7 digit member IDs included
  • (Warn that a memberID has 7 characters; return which memberID is the 7 character one; suggest that you dropped a character or may need to add a leading 0)