databases/py-sqlalchemy-migrate: Add sqlparse and six dependencies

Both sqlparse and six are mentioned as dependencies, but are missing in
the ports RUN_DEPENDS.

The missing sqlparse dependencies causes (at least) devel/buildbot to
generate an error at run-time [1].

This change adds sqlparse and six to RUN_DEPENDS.

While I'm here:

• Add LICENSE_FILE
• Update RUN_DEPENDS version specs to match upstream files (NOOP)
• Enable "concurrent" Python version installation
• Add NO_ARCH (architecture independent)

PR: 215273 [1]
Reported by: Nikola Kolev <koue chaosophia net>
Approved by: portmgr (blanket)
MFH: 2016Q4