biology/py-biopython: Unbreak on python3; Add license

Two items prevented python3 compatibility:

• Breakage of ASCII codec due to non-ascii characters in README: https://github.com/biopython/biopython/issues/1649
• The outdated dependency: print/py-reportlab1 instead of the modern version 3.X print/py-reportlab

Port changes:

• USES=python:2.7 -> USES=python
• Add pre-configure that clears the README file
• Add LICENSE/LICENSE_FILE

Testing:

• Ran the tutorial testcase http://biopython.org/DIST/docs/tutorial/Tutorial.html, particularly pdf writing through print/py-reportlab worked fine.

Asked the upstream to clarify the acceptable dependency version: https://github.com/biopython/biopython/issues/1650

Approved by: portmgr blanket (unbreak for python3; add license)