improve handling of non-finite floating point values (#490)

* improve HTTP error reporting

* generate standards-compatible JSON

* add --nan-to-num work-around for non-finite floating point values

* lint

* update tests

* correctly set Infinities to min/max

* REAMDE update for --nan-to-num

* define constant for repetitive warning message

* clarify where NaN errors will occure

server/test/test_scanpy_engine.py

@@ -14,7 +14,8 @@ from server.app.scanpy_engine.scanpy_engine import ScanpyEngine
 class UtilTest(unittest.TestCase):
     def setUp(self):
         args = {'layout': 'umap', 'diffexp': 'ttest', 'max_category_items': 100,
-                'obs_names': None, 'var_names': None, 'diffexp_lfc_cutoff': 0.01}
+                'obs_names': None, 'var_names': None, 'diffexp_lfc_cutoff': 0.01,
+                'nan_to_num': True}
 
         self.data = ScanpyEngine("example-dataset/pbmc3k.h5ad", args)
         self.data._create_schema()