Motions: Add new filter 'Is not an amendment'

[MSoeb]

Current behavior
If a user wants to create a pdf export of all final versions without amendments, it is necessary to set two filters to get a clean motion list. The user has to select in the amendment filter 'Has amendments' and 'Is no amendment and has no amendments'. This is not intuitive.

Wanted behavior
A new filter should be added, that shows ALL motions without amendments. This would help a lot. The filter should be named 'Is not an amendment'. It should be placed at the second position in the red square.