added cancel button to mfa.auth, closes #30

uffd/mfa/templates/auth.html

@@ -35,6 +35,9 @@
 		<div class="form-group col-12">
 			<button type="submit" class="btn btn-primary btn-block">Verify</button>
 		</div>
+		<div class="form-group col-12">
+			<a href="{{ url_for("session.logout") }}" class="btn btn-secondary btn-block">Cancel</a>
+		</div>
 	</div>
 </div>
 </form>