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

test/__init__.py

@@ -0,0 +1,11 @@
+import random
+import string
+from os import popen
+
+PROJECT_ROOT = popen("git rev-parse --show-toplevel").read().strip()
+FIXTURES_ROOT = PROJECT_ROOT + "/test/fixtures"
+H5AD_FIXTURE = FIXTURES_ROOT + "/pbmc3k-CSC-gz.h5ad"
+
+
+def random_string(n):
+    return "".join(random.choice(string.ascii_letters) for _ in range(n))