Change default title for motion polls

[Elblinator]

Currently:
If you create a motion-poll then the first poll's default title is "Vote", afterwards the default title is "Vote (#)"

The default title is the title which is per default displayed in the dialog to create a new motion-poll

Wanted:

• The new default title should be "Motion Motion-Nr# Vote:", if there is already a motion-poll then the default title should be "Motion Motion-Nr# Vote (#):"

• If the motion doesn't have a Motion-Nr then the title should be "Motion Vote:"