core library (#711)

* move app creation to function

* create engine without load

* flake 8 fixes

* cleanup original scanpy test

* add default config

* handle missing data

* test data changes

* unify update

* load data isn't static anymore

* make app a class

server/app/util/constants.py

@@ -30,3 +30,4 @@ class DiffExpMode(AugmentedEnum):
 JSON_NaN_to_num_warning_msg = (
     "JSON encoding failure - please verify all data are finite values (no NaN or Infinities)"
 )
+REACTIVE_LIMIT = 1_000_000