Fixed #1190: Wrong sorting of motion identifier

- Added natural sorting JS plugin for motion DataTables (column identifier).
- Added the new requirements python package 'natsort' for natural sorting of motions in PDF.
Merge pull request #1192 from emanuelschuetze/naturalsort

Fixed #1190: Wrong sorting of motion identifier
Fixed #1138: Wrong file for projectors logo
Merge pull request #1207 from emanuelschuetze/fix-1138

Fixed #1138: Wrong file for projectors logo
Reinserted icon and link for preview of agenda slide. Fixed #1199.
Merge pull request #1211 from normanjaeckel/PreviewAgenda

Reinserted icon and link for preview of agenda slide. Fixed #1199.
fix for python2.6 and pip 1.5
Merge pull request #1218 from ostcar/argparse_fix

Fix for Python 2.6 and Pip 1.5 (use of argparse 1.2.1)
Merge remote-tracking branch 'openslides/stable/1.5.x'

Conflicts:
	extras/win32-portable/create_portable.txt
	extras/win32-portable/prepare_portable.py
	openslides/motion/templates/motion/motion_list.html
	openslides/projector/templates/projector.html
	requirements_production.txt