Standardize license to GPL v2 across all files

Fixes conflicting license statements by consistently using GPL v2:
- Updated setup.py classifier and keyword to specify GPL v2
- Changed pywebdav/__init__.py license from LGPL v2 to GPL v2
- Replaced doc/LICENSE with GPL v2 license text
- Updated README.md to correctly reference GPL v2

Resolves #49

Author: pi-anl

README.md

@@ -81,7 +81,7 @@ REQUIREMENTS
 LICENSE
 -------
 
-General Public License v2
+GNU General Public License v2
 see doc/LICENSE