Toggleable interactivity during edit mode

[LeonMatthes]

As a presentation creator, I want to be able toggle interactivity in edit mode in order to easier layout my slides.

Acceptance criteria:

• [ ] Similar to the snap button, an interactivity toggle button exists
• [ ] When interactivity is disabled, slide content does not receive events
• [ ] Slide content can now be dragged via drag & drop

[LeonMatthes]

Estimated effort: 8

[LeonMatthes]

No longer necessary, as it is now possible to grab a Morph directly at its border