When use_annotations = T, error is thrown
**Describe the bug**
When using the shiny app configured to retrieve annotations with getModelManifest, app breaks with following error: 

```
Warning: Error in py_call_impl: NameError: name 'syn_store' is not defined

Detailed traceback: 
  File "/home/rallaway/miniconda3/envs/data_curator_env_oauth/lib/python3.7/site-packages/schematic/models/metadata.py", line 149, in getModelManifest
    dataset_id=datasetId, json_schema=jsonSchema, sheet_url=sheetUrl
  File "/home/rallaway/miniconda3/envs/data_curator_env_oauth/lib/python3.7/site-packages/schematic/manifest/generator.py", line 976, in get_manifest
    annotations = syn_store.getDatasetAnnotations(dataset_id)
```
I've omitted the rest of the bug report template for now because I think it's a simple fix and will try and do it now. :)
diff --git a/schematic/manifest/generator.py b/schematic/manifest/generator.py
index 5dd3e33e..86adb7ae 100644
--- a/schematic/manifest/generator.py
+++ b/schematic/manifest/generator.py
@@ -973,7 +973,7 @@ class ManifestGenerator(object):
             # entities to files and folders (ignoring tables/views)
             annotations = pd.DataFrame()
             if self.is_file_based:
-                annotations = syn_store.getDatasetAnnotations(dataset_id)
+                annotations = store.getDatasetAnnotations(dataset_id)
 
             # Subset columns if no interested in user-defined annotations
             if self.is_file_based and not self.use_annotations:
['schematic/manifest/generator.py']