Meta-issue for cleaning up blockItems

[ahobeost]

• [ ] reduce duplication through inheritance, or extracting classes/methods (composition over inheritance)
• [ ] provide prefix in the child class and not the factory < remove displaynamePrefix as argument
• [ ] duplicate prefix for HP hptwoHX, and IceStorage IceStorage2HX (ask Dani)
• [ ] tests whether all prefixes are unique
• [ ] deal with loadedBlock < based on whether displayName is None
• [ ] move files into blockItem directory
• [ ] remove editor from blockItem
• [ ] remove editor from child classes
• [x] projectPath vs. folderPath. Only one should be used

[ahobeost]

projectPath was still being used by two methods of the Editor. They have been adjusted to folderPath in #410.