Refactor czi_hosted and server into backend directory, pull common code into backend/common, refactor tests (#2102)

* move local_server -> backend/server server-> backend/czi_hosted, pull common code into backend/common update imports, tests and make commands

server/requirements.txt

@@ -1,27 +0,0 @@
-anndata>=0.7.0
-boto3>=1.12.18
-click>=7.1.2
-fastobo>=0.6.1
-Flask>=1.0.2
-Flask-Compress>=1.4.0
-Flask-Cors>=3.0.6
-Flask-RESTful>=0.3.6
-flask-server-timing>=0.1.2
-flask-talisman>=0.7.0
-flatbuffers>=1.11.0
-flatten-dict>=0.2.0
-fsspec>=0.4.4,<0.8.0
-gunicorn>=20.0.4
-h5py<3.0.0 # h5py>=3.0.0 had a breaking change; there is a fix in anndata>=0.7.5
-numba>=0.49.1,<0.53.0
-numpy>=1.15.0
-packaging>=20.0
-pandas>=1.0,!=1.1  # pandas 1.1 breaks tests, https://github.com/pandas-dev/pandas/issues/35446
-PyYAML>=5.3
-scipy>=1.0
-requests>=2.22.0
-tiledb>=0.5.9,>=0.6.2,!=0.7.2
-s3fs==0.4.2
-scanpy==1.4.6 # Until we move to anndata 0.7.4 scanpy needs to be pinned here
-sqlalchemy>=1.3.18
-umap-learn<0.5.0 # The pinned version scanpy is not compatible with latest umap-learn