fix: ManyToMany Scrolling

[ZairMahmood]

Problem:

• ManyToMany field in changeview is broken

For issue #376

Solution:

• Create a new class (MULTIPLE_SELECT_CLASSES)
  • remove the truncate class
  • add the overflow-y-auto

[lukasvinclav]

Hey, thanks for PR which pointed me at the right direction. I created new PR #421 fixing the issue.