Rework App modes

- Replace App mode constants with capability-based flags
- Add App->isInstallMode()
- Add file config fallback in (P)Config abstraction
- Removed logger disabling code

bin/daemon.php

@@ -28,7 +28,7 @@ require_once "include/dba.php";
 
 $a = new App(dirname(__DIR__));
 
-if ($a->mode === App::MODE_INSTALL) {
+if ($a->isInstallMode()) {
 	die("Friendica isn't properly installed yet.\n");
 }