Hide some segment context menu actions

[dieknolle3333]

I may have found two bugs regarding the segment context menu in the viewport.

Context 1

I opened an annotation for dataset l4_sample_remote_zarr and made all layers except the skeleton layer invisible.

Expected Behavior 1

I don't think I should see mesh related actions, such as "Compute mesh" or "Flood-fill segment".

Current Behavior 1

Context 2

• See picture, not sure what exactly needs to be done to get to this state
• I clicked "Select segment", which activates the segment (although brush tool is disabled)

Expected Behavior 2

Context entry shoudnt be there if brush tool is disabled

Current Behavior 2

toast occurs

Steps to Reproduce the bug

• Cannot reproduce the bug anymore / needs deeper investigation. (second case)

Your Environment for bug

• Browser name and version: e.g. Chrome 39
• Operating System and version: e.g. Windows 10
• Version of WEBKNOSSOS (Release or Commit):
  • first bug webknossos.org (probably b274c45), second bug locally with master commit 883f955