Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/test/fixtures/test_config.yaml

@@ -0,0 +1,34 @@
+fixup_gene_symbols:
+    X: log1p
+obs:
+    cell_type_ontology_term_id:
+        louvain:
+            CD4 T cells: CL:00001
+            B cells: CL:00002
+            CD14+ Monocytes: CL:00003
+            NK cells: CL:00004
+            CD8 T cells: CL:00005
+            FCGR3A+ Monocytes: CL:00006
+            Dendritic cells: CL:00007
+            Megakaryocytes: CL:00008
+    tissue_ontology_term_id: UBERON:12345
+    assay_ontology_term_id: EFO:12345
+    disease_ontology_term_id: MONDO:12345
+    ethnicity_ontology_term_id: HANCESTRO:12345
+    development_stage_ontology_term_id: HsapDv:12345
+    sex: other
+uns:
+    version:
+        corpora_schema_version: 1.0.0
+        corpora_encoding_version: 0.1.0
+    organism_ontology_term_id: NCBITaxon:9606
+    title: Test dataset
+    contributors:
+        - name: Marcus
+          institution: CZI
+    layer_descriptions:
+        X: raw
+    project_links:
+        - link_url: https://chanzuckerberg.com/
+          link_name: CZI
+          link_type: SUMMARY