refactor config to support different config options for datasets in different dataroots. (#1596)

This will give us the ability to specify different config options for
different dataroots.

the key of the dataroot dictionary is no longer the same as the dataroot_url.
Previously key==dataroot_url, and now those are separated.

Added an "is_multi_dataset" function to simplify logic where it branched on single vs multi.

Simplified the rest.py interface by no longer passing in the user annotations object, since
that can be retrieved from the dataset.

server/test/test_matrixcache.py

@@ -21,13 +21,13 @@ class MatrixCacheTest(unittest.TestCase):
             shutil.copytree(source, target)
 
     def use_dataset(self, matrix_cache, dirname, app_config, dataset_index):
-        with matrix_cache.data_adaptor(os.path.join(dirname, str(dataset_index) + ".cxg"), app_config) as adaptor:
+        with matrix_cache.data_adaptor(None, os.path.join(dirname, str(dataset_index) + ".cxg"), app_config) as adaptor:
             pass
         return adaptor
 
     def use_dataset_with_error(self, matrix_cache, dirname, app_config, dataset_index):
         try:
-            with matrix_cache.data_adaptor(os.path.join(dirname, str(dataset_index) + ".cxg"), app_config):
+            with matrix_cache.data_adaptor(None, os.path.join(dirname, str(dataset_index) + ".cxg"), app_config):
                 raise DatasetAccessError("something bad happened")
         except DatasetAccessError:
             # the MatrixDataCacheManager rethrows the exception, so catch and ignore
@@ -38,7 +38,7 @@ class MatrixCacheTest(unittest.TestCase):
         result = {}
         for k, v in datasets.items():
             # filter out the dirname and the .cxg from the name
-            newk = int(k[len(dirname) + 1 : -4])
+            newk = int(k[1][len(dirname) + 1 : -4])
             result[newk] = v
 
         return result