[Super Voxel Editing] Reset skeletons/meshes after successful mergers/split

[hotzenklotz]

Detailed Description

When doing any manipulations to the super voxel graph, a lot of agglomerate skeletons and mesh are being loaded and displayed. Once I am done working on a pair of segments, there should be any easy way to "reset the scene", i.e. unloaded the skeletons and mesh to have a fresh slate for the next manual fix I want to do.

Context

• [ ] Specific to long-running jobs (set jobsEnabled=true in application.conf)
• [ ] Specific to webKnossos.org (set isDemoInstance=true in application.conf)