devel/py-virtualenvwrapper: Update to 4.7.1

• Update PORTVERSION and distinfo checksum (4.7.1)
• Remove *_DEPENDS versions (no longer version specific upstream)
• Add support for concurrent (Python 2/3) use
• Update sphinx docs output directory
• Convert all conditionals to options helpers

Approved by: nivit (maintainer)
Differential Revision: https://reviews.freebsd.org/D3539