GUI editor (further refinements)
Following https://gitlab.com/groups/appsemble/-/epics/11:
## Beta 2:
### Breaking bugs
- [x] Fix all bugs in the breaking category appsemble#1125
### Code cleanup
- [x] Finish refactoring tasks appsemble#1171
- [ ] appsemble#1156
- [x] appsemble#1132
### New app preview features:
- [x] New app preview that allows editing through mouse interaction https://gitlab.com/appsemble/appsemble/-/issues/1016
- [x] Clicking blocks brings up their property menu https://gitlab.com/appsemble/appsemble/-/issues/1016
- [x] Dragging implemented blocks changes their order in the app definition https://gitlab.com/appsemble/appsemble/-/issues/1016
- [x] Block highlighting on hover https://gitlab.com/appsemble/appsemble/-/issues/1016
### Block adding features:
- [x] Better defaults for all blocks appsemble#1193
- [x] Nicer block store (two columns and thumbnail pictures) appsemble#1176
- [x] 3d party blocks in block store appsemble#1176
### Resources tab
- [ ] Creating resources by GUI (https://gitlab.com/appsemble/appsemble/-/issues/837)
- [ ] Editing existing resources
epic