Fixed #551: Used unicode font for circle in ballot pdf. Removed pillow.

That fixed also #1140 (Server error when trying to view ballot paper pdf)
Merge pull request #1215 from emanuelschuetze/fix-551

Removed pillow. Used unicode circle font. (Fixed #551 and #1140)
Merge commit '7addd69050a69b9d02aacba116939829497ca338' into MergeStablePart2

Conflicts:
	extras/win32-portable/create_portable.txt
	extras/win32-portable/prepare_portable.py
	openslides/assignment/views.py
	openslides/core/static/img/circle.png
	openslides/motion/pdf.py
	openslides/utils/pdf.py
Merge pull request #1244 from emanuelschuetze/MergeStablePart2

Merge stable branch (part 2)