[WIP] Implemented basic permissions (#960)

* Add permissions to Database & add "User"-classes

* Add UI & API for Permissions, protect "User"-(Api)-Controller with new permissions.

* Add some permissions.

* Add permission localization

* Add error handling.

* Error pages: only redirect on 404

* ExceptionController: return JSON-Response on api-routes

* Rename PRODUCT_ADD to PRODUCT_PURCHASE

* Move translation to new file

* Fix checkboxes stay selected on reload.

* Remove configurable User-implementation

* Remove MASTER_DATA_READ

* Disable buttons the user isn't allowed to use.

* Add default permissions for new users

* When migration to permissions, everyone starts as ADMIN

* Permission-Localization: add to transifex & LocalizationService

* Review

Co-authored-by: Bernd Bestel <bernd@berrnd.de>

views/errors/500.blade.php

@@ -0,0 +1,16 @@
+@extends('errors.base')
+
+@section('title', $__t('Server error'))
+
+@section('content')
+    <div class="row">
+        <div class="col">
+            <div class="alert alert-danger">{{ $__t('A server error occured while processing your request') }}</div>
+			<div class="alert alert-warning">
+				{{ $__t('If you think this is a bug, please report it') }}<br>
+				&rarr; <a target="_blank" href="https://github.com/grocy/grocy/issues">https://github.com/grocy/grocy/issues</a>
+			</div>
+		</div>
+	</div>
+	@parent
+@stop