Add "block drafts" feature

Design doc:
https://docs.google.com/document/d/16AX1tKa1CGSWwZtbW42h1uHy8SEPuv1ZjT_oHxc0UUI/edit

Fixed: twpowertools:84
Change-Id: Ibb172113774c5e2cab14e3d87a178bafed85df0b
diff --git a/src/static/rulesets/blockDrafts.json b/src/static/rulesets/blockDrafts.json
new file mode 100644
index 0000000..1d58538
--- /dev/null
+++ b/src/static/rulesets/blockDrafts.json
@@ -0,0 +1,9 @@
+[{
+    "id": 1,
+    "action": {
+        "type": "block"
+    },
+    "condition": {
+        "urlFilter": "||support*.google.com/s/community/api/*DraftMessage"
+    }
+}]