Tools for configuring AWS credentials in MQTT Mutual Auth Demo (#370)

This adds aws_config_offline, which allows the user to download demo_config.h for the MQTT Mutual Auth Demo using a webpage.
This also adds aws_config_quick_start, which provides a means to generate demo_config.h for the Mutual Auth Demo with boto3.

tools/aws_config_quick_start/thing.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+
+import boto3
+import json
+
+
+class Thing():
+    def __init__(self, name):
+        self.client = boto3.client('iot')
+        self.name = name
+        self.arn = ''
+
+    def create(self):
+        assert not self.exists(), "Thing already exists"
+        result = self.client.create_thing(thingName=self.name)
+        self.arn = result['thingArn']
+
+    def delete(self):
+        assert self.exists(), "Thing does not exist"
+        principals = self.list_principals()
+        for principal in principals:
+            self.detach_principal(principal)
+        self.client.delete_thing(thingName=self.name)
+
+    def exists(self):
+        list_of_things = self.client.list_things()['things']
+        for thing in list_of_things:
+            if thing['thingName'] == self.name:
+                return True
+        return False
+
+    def attach_principal(self, arn):
+        assert self.exists(), "Thing does not exist"
+        self.client.attach_thing_principal(thingName=self.name, principal=arn)
+
+    def detach_principal(self, arn):
+        assert self.exists(), "Thing does not exist"
+        self.client.detach_thing_principal(thingName=self.name, principal=arn)
+
+    def list_principals(self):
+        assert self.exists(), "Thing does not exist"
+        principals = self.client.list_thing_principals(thingName=self.name)
+        principals = principals['principals']
+        return principals