python: Rename compiled SWIG module.

Avoid the name pygpgme, as this is the name of another popular Python
binding for GPGME.

This commit renames the compiled Python module produced by SWIG.

• lang/python/Makefile.am: Rename the compiled Python module.
• lang/python/gpgme.i: Likewise.
• lang/python/pyme/core.py: Likewise.
• lang/python/pyme/errors.py: Likewise.
• lang/python/pyme/util.py: Likewise.
• lang/python/pyme/version.py.in: Likewise.
• lang/python/setup.py.in: Likewise.

• Signed-off-by: Justus Winter <justus@g10code.com>