#31 ability to 'message to user' when sharing to externals

[Nick Silkey]

When you share a file with an external party, it would be valuable to let the sharer provide some context behind the file share ('this is version 12 of the foobar document ; this is the library late fee receipt for your interlibrary loan ; etc).

While its possible for sharers to stupidly put a password in said field, thats an acceptable risk which could be countered with big flags on the share of 'dont even think of putting the share password here!'.