Put get_channel_by_name back in (#243)

Need this to support admin !join command

Need that to debug private channels when the bot breaks

Author: l4cr0ss

util/slack_wrapper.py

@@ -208,3 +208,10 @@ def remove_reminders_by_text(self, text: str):
         for reminder in reminders.get("reminders", []):
             if text in reminder["text"]:
                 self.remove_reminder(reminder["id"])
+
+    def get_channel_by_name(self, name):
+        """Fetch a channel with a given name."""
+        channels = self.get_channels(types="public_channel,private_channel")
+        for channel in channels:
+            if channel['name'] == name:
+                return channel