move common code into server, update tests and makefile (#2425)

* move common code into server, update tests and makefile

remove backend directory, refactor

update smoke tests

server/common/constants.py

@@ -0,0 +1,35 @@
+from enum import Enum
+
+
+class AugmentedEnum(Enum):
+    def __hash__(self):
+        return self.value.__hash__()
+
+    def __eq__(self, other):
+        if isinstance(other, type(self)) or isinstance(other, str):
+            return self.value == other
+        return False
+
+    def __str__(self) -> str:
+        return self.value
+
+
+class Axis(AugmentedEnum):
+    OBS = "obs"
+    VAR = "var"
+
+
+class DiffExpMode(AugmentedEnum):
+    TOP_N = "topN"
+    VAR_FILTER = "varFilter"
+
+
+class XApproximateDistribution(AugmentedEnum):
+    NORMAL = "normal"
+    COUNT = "count"
+
+
+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
+
+MAX_LAYOUTS = 30