net-im/py-unmessage: Add missing dependencies

unmessage currently fails at runtime with the following errors:

1. pkg_resources.DistributionNotFound: The 'service_identity' distribution was not found and is required by Twisted

unmessage depends on Twisted *and* its "tls" optional (extras_require)
dependencies, requiring unmessage to depend directly on them:

• openssl
• service_identity
• idna

2. ImportError: No module named _sqlite3 (fixed by ports r512099)

3. File "/usr/local/lib/python2.7/site-packages/unmessage/gui.py", line 5, in <module> import Tkinter as Tk

Add dependency on x11-toolkits/py-tkinter accordingly

While I'm here:

Pet portlint: extra item in USES/USE_x section: "NO_ARCH".

[1] setup.py: install_requires: 'Twisted[tls]>=16.6.0',

Reported by: DanDare (via IRC)
Approved by: portmgr (blanket(s): missing dependencies, ports compliance)
MFH: 2019Q3