Adds Office 365 / Outlook.com Calendar Integration

* Added MS_GRAPH_CLIENT_* credentials to .env.example.
* Refactored the google integration into an abstraction layer for creating events and getting the user schedule from either Google or Office 365.
* FIX: when re-authorizing the Google Integration the refresh_token would no longer be set and the google integration would stop working.
* Updated Office 365 integration image

.env.example

@@ -1,3 +1,7 @@
-DATABASE_URL='postgresql://<user>:<pass>@<db-host>:<db-port>'
-GOOGLE_API_CREDENTIALS='secret'
-NEXTAUTH_URL='http://localhost:3000'
+DATABASE_URL='postgresql://<user>:<pass>@<db-host>:<db-port>'
+GOOGLE_API_CREDENTIALS='secret'
+NEXTAUTH_URL='http://localhost:3000'
+
+# Used for the Office 365 / Outlook.com Calendar integration
+MS_GRAPH_CLIENT_ID=
+MS_GRAPH_CLIENT_SECRET=