Restore form editor from history

[japsu]

In order not to make this a forever-running PR, let's try to merge a partial implementation. TODO for that:

• [x] do the needful so that it compiles (`npm run build´)
  • need not be pretty; those pesky components that currently typeerror are not yet mounted anywhere
• [x] disable the create language version button for which there is not yet implementation

Features for #386 #403 and further work:

• [x] create survey
• [x] change settings of survey
  • [ ] allow changing anonymity only if there are no responses (currently not shown on form) #402
  • [ ] better feedback for submitting the form #376
  • [ ] confirm navigation if unsaved changes
• [x] delete a survey
  • [X] ask for confirmation for removal
  • [X] forbid deleting a survey that has language versions
  • [ ] soft delete for all surveys/surveys with responses? (mark as deleted, don't really delete) #432
• [ ] make dimension editor a tab of the survey editor
• [x] open and close the survey for responses
• [ ] add a language version
• [x] edit title and description of a language version
  • [ ] better feedback for submitting the form #376
• [ ] edit fields of a language version
• [ ] remove a language version
  • [ ] ask for confirmation for removal
  • [ ] forbid removal of a language version using which a response has been made
  • [ ] soft delete? (mark as deleted, don't really delete) #432