BibCatalog: fix bug with multi-line ticket body

• Fixes an issue causing ticket submission to fail when attempting to submit a ticket with a multi-line text. With these changes ticket_submit() does no longer accept newlines for parameter 'text'.

• Re-factors larger parts of the RT class and adds new function to add comments on tickets, ticket_comment(), which do accept multi-line text.

• Removes un-used configuration variable CFG_BIBCATALOG_QUEUES. (fixes #746)