rename variables in UI and start as regular regionprops

[zoccoler]

• change initial state of widgets to start as regular regionprops
• rename Menu entry
• rename 'things_inside_things' label to 'relate to other channel(s)'
• update notifications accordingly
• add layer names to test file
  • tests were failing locally because layer names were 'Image', 'Image [1]' etc instead of using variable names
  • this was making assert statements fail because table column names rely on layer names
  • explicitly specifying layer names avoids this