Implement Hook::callAll('storage_instance') call for addons and add a description for it.

- Remove implicit Dice usage
- Add concrete instance creating
- Adding Hook call for addon instance creating
- Updating doc for Hook
- Updating tests

tests/Util/SampleStorageBackendInstance.php

@@ -0,0 +1,18 @@
+<?php
+
+// contains a test-hook call for creating a storage instance
+
+use Friendica\App;
+use Friendica\Core\L10n\L10n;
+use Friendica\Test\Util\SampleStorageBackend;
+use Mockery\MockInterface;
+
+function create_instance(App $a, &$data)
+{
+	/** @var L10n|MockInterface $l10n */
+	$l10n = \Mockery::mock(L10n::class);
+
+	if ($data['name'] == SampleStorageBackend::getName()) {
+		$data['storage'] = new SampleStorageBackend($l10n);
+	}
+}