Make trigger raise message more clear

[andreasknoepfle]

Hello,

we just debugged a bit on a missing Carbonite.insert_transaction since the raised message from the DB about the FK constraint does not clearly say "carbonite" on it.

Since one just sees:

Postgrex.Error) ERROR 23503 (foreign_key_violation) DELETE on table foo.bar without prior INSERT into foo.transactions

it only indicated that it is carbonite related, once you have a better look at where the transactions table comes from. Someone that doesn't know carbonite so well might think that this is an internal postgres table or something else.

Maybe we can add "from one of your carbonite triggers" to the raise message to make it clear for everyone what to search for.

Wdyt @maltoe