refactor: replace custom CRM with Monica fork

app/Http/Controllers/DAV/Backend/IDAVBackend.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Http\Controllers\DAV\Backend;
+
+interface IDAVBackend
+{
+    /**
+     * Returns the uri for this backend.
+     *
+     * @return string
+     */
+    public function backendUri();
+
+    /**
+     * Returns the object for the specific uuid.
+     *
+     * @param  string|null  $collectionId
+     * @param  string  $uuid
+     * @return mixed
+     */
+    public function getObjectUuid($collectionId, $uuid);
+
+    /**
+     * Returns the collection of objects.
+     *
+     * @param  string|null  $collectionId
+     * @return \Illuminate\Support\Collection
+     */
+    public function getObjects($collectionId);
+
+    /**
+     * Returns the extension for this backend.
+     *
+     * @return string
+     */
+    public function getExtension();
+}