textproc/py-sphinxcontrib-bitbucket: Fix Python 3 build/run

Fix Python 3 build, identified while testing devel/py-virtualenvwrapper:

Exception occurred:

File "/usr/local/lib/python3.7/site-packages/sphinx/registry.py", line 196, in load_extension
  mod = __import__(extname, None, None, ['setup'])
File "/usr/local/lib/python3.7/site-packages/sphinxcontrib/bitbucket.py", line 26
  except AttributeError, err:
                       ^

SyntaxError: invalid syntax

While I'm here, level up ports/python compliance:

• Add python to CATEGORIES
• Add LICENSE/LICENSE_FILE
• Add NO_ARCH
• Add missing RUN_DEPENDS
• Correct RUN_DEPENDS version-specs

Approved by: portmgr (blanket(s): build fix, ports compliance, dependencies)
MFH: 2019Q3