Add get_win32_portable_user_data_path() function in main.py to return
correct user data path ("/openslides") of portable version.
Automatically load plugins from portable plugins dir; closes #1178

All modules/ packages in the openslides/plugins subdirectory of the
portable version will be automatically added to INSTALLED_PLUGINS
Update copyright to 2014
Portable: Create empty plugins directory.

Fixed file permissions.
Merge pull request #1270 from emanuelschuetze/fix1178

Adds plugin directory for win32 portable version (Fixed #1178).
Updated CHANGELOG, README.rst, requirements files, .travis.yml and setup.py.