FEATURE #1368: add form for creating new custom field

Currently, form is not saved, however it is validated.

resources/lang/en/admin/customFields.php

@@ -1,7 +1,17 @@
 <?php
 return [
-  'overview' => 'List of all custom fields',
-  'noFields' => 'No custom fields defined.',
-  'users' => 'Custom fields for user',
-  'content' => 'Custom fields for content page',
+    'overview' => 'List of all custom fields',
+    'new'      => 'New custom field',
+    'noFields' => 'No custom fields defined.',
+    'users'    => 'Custom fields for user',
+    'content'  => 'Custom fields for content page',
+    'name' => 'Name',
+    'description' => 'Description',
+    'type' => 'Type of custom field',
+    'required' => 'Is field required?',
+    'defaultValue' => 'Default value',
+    'regExp' => 'Match only this regular expression',
+    'minLength' => 'Minimum length',
+    'maxLength' => 'Maximum length',
+    'createNew' => 'Create new field'
 ];