Add file mime type

apps/workflowengine/css/admin.css

apps/workflowengine/js/admin.js

apps/workflowengine/js/filemimetypeplugin.js

apps/workflowengine/js/filesizeplugin.js

apps/workflowengine/js/filesystemtagsplugin.js

apps/workflowengine/js/usergroupmembershipplugin.js

apps/workflowengine/lib/AppInfo/Application.php

apps/workflowengine/lib/Check/AbstractStringCheck.php

apps/workflowengine/lib/Check/FileMimeType.php

apps/workflowengine/tests/Check/AbstractStringCheckTest.php