net-p2p/transmission: Reorganize as a metaport

Port reorganized as a metaport. Each component can be installed
separately or selected as an option via the metaport. Components
were moved to net-p2p/transmission-components.
See MOVED for additional information.

Also fixes log-level typo in rc file and description errors

PR: 273841, 274054 274065
Reported by: Anton Saietskii <vsasjason@gmail.com>
Reported by: Matt <lazeraman@gmail.com>
Reported by: Benjamin Takacs <nimaje+fbz@bureaucracy.de>
Differential Revision: https://reviews.freebsd.org/D41975