Make "unfollow" undo pending outgoing follow request too (#4781)

* Make "unfollow" undo pending outgoing follow request too

* Add cancel button to web UI when awaiting follow request approval

* Make the hourglass button do the cancelling

app/javascript/mastodon/locales/defaultMessages.json

@@ -436,7 +436,7 @@
         "id": "account.follow"
       },
       {
-        "defaultMessage": "Awaiting approval",
+        "defaultMessage": "Awaiting approval. Click to cancel follow request",
         "id": "account.requested"
       },
       {

app/javascript/mastodon/locales/en.json

@@ -12,7 +12,7 @@
   "account.mute": "Mute @{name}",
   "account.posts": "Posts",
   "account.report": "Report @{name}",
-  "account.requested": "Awaiting approval",
+  "account.requested": "Awaiting approval. Click to cancel follow request",
   "account.share": "Share @{name}'s profile",
   "account.unblock": "Unblock @{name}",
   "account.unblock_domain": "Unhide {domain}",