next beta release

[jerch]

beta wishlist:

• [x] type hints and sanity checks #86
• [x] fix up pulling ambiguity #93
• [ ] ~reduce "transactional pressure" to one transaction at top level~ postponed
• [x] remove multi variants #57
• [x] ~rework transitive reduction in intermodel deps (partially done in #53)~ dealt with in #114
• [x] fast_update option (alpha) #97
• [x] transit to django-fast-update package
• [x] fix proxy models #109
• [x] F expression clarification #98
• [x] remove obsolete optimizations (createmap & TR in intermodel graph) #114
• [x] better update planning for updatedata #32
• [ ] ~support some sort of update signals #58~ postponed
• [x] convenient symbol access
  • [x] place __all__ into models.py
  • [x] make underlying graphs easier accessible from shell (lazy loading function?)
• [x] remove Django 2.2 shims
• [x] cleanup docs (also add #90)

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Edit: Postponed several aspects to not to delay the release too much because of only half-finished things.