Re-added port: textproc/ibus-m17n: m17n IM engine for IBus framework (existed 2009/09/04-2017/04/30, deleted in r439826)

It has been deleted due to the Google Code closure.
It allows to use keyboard layouts of the m17n project
through standard IBus interface.

Approved by: adamw (mentor)
Differential Revision: https://reviews.freebsd.org/D13548