add template folder CRUD

* create template folder
* rename template folder
* get list of template folders for service (not nested/presented in any
  particular way)
* delete template folder

Also removed `lazy=dynamic` from the `template_folder.templates`
relationship. lazy=dynamic returns a query object (which you can then
filter further). We just want to return the entire fetched list, at
least for now.

app/template_folder/template_folder_schema.py

@@ -0,0 +1,22 @@
+from app.schema_validation.definitions import nullable_uuid
+
+post_create_template_folder_schema = {
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "description": "POST schema for getting template_folder",
+    "type": "object",
+    "properties": {
+        "name": {"type": "string", "minLength": 1},
+        "parent_id": nullable_uuid
+    },
+    "required": ["name", "parent_id"]
+}
+
+post_rename_template_folder_schema = {
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "description": "POST schema for renaming template_folder",
+    "type": "object",
+    "properties": {
+        "name": {"type": "string", "minLength": 1},
+    },
+    "required": ["name"]
+}