Updating D41975: net-p2p/transmission: Reorganize as a metaport

1. -Added docs flavor -Revised per fuz

Updating D41975: net-p2p/transmission: Reorganize as a metaport

1. Added flavor-specific options files, fixed option descriptions.

In D41975#957578, @vsasjason_gmail.com wrote:

After carefully reading bsd.options.mk I came to following coclusions (but I may be wrong):

1. OPTIONS_FILE being crafted from <category>/<portname>, which means we can't really define any options inside flavors, but in root of Makefile only [...]

I'm unsure where to put DOCS option though. It would be nice to install it with any of flavors, but there will be a conflict then...
Also, it seems reasonable to me install GUI not as bin/transmission-{gtk|qt}, but as bin/transmission (of course, then respective OPTION should be changed to RADIO and conflicts between default, gtk, and qt flavors should be registered.

Updating D40910: net-p2p/transmission: Update 3.00 -> 4.0.4 & modernize port.

Updating D40910: net-p2p/transmission: Update 3.00 -> 4.0.4 & modernize port.

net-p2p/libutp: fix patch

Corrected typo; rely on bsd.port.mk to specify build type

Further revisions to conform to prior slave port style; fix distfile

net-p2p/transmission: revise to conform

Arc diff did not like my rebase. Apologies for the spam.

Requesting review from @tcberner.

In D40910#931168, @fcharlier_ploup.net wrote:

• net-p2p/transmission: rm old web slave port