added docstrings to event controller and moved constants

server/app/constants/__init__.py

@@ -0,0 +1,9 @@
+ALLOWED_FILES_TYPES = ["image/jpeg", "image/png"]
+ONE_MB = 1000000
+
+# sql table names
+SERIES_TABLE = "series"
+EVENT_TABLE = "events"
+GROUP_TABLE = "group_table"
+MUSICIAN_TABLE = "musicians"
+USER_TABLE = "users"