tyalpha: support opacity level option

Summary:
support opacity level option for tyalpha.

usage: tyalpha [-p] on|off|<opacity level>

Test Plan: terminology -> tyalpha 60

Reviewers: billiob, raster

Subscribers: seoz

Differential Revision: https://phab.enlightenment.org/D1197
mailmap: added Wonguk Jeong's information.