copy all files to TimesheetCategoryBundle in var/plugins/
var/plugins/
├── TimesheetCategoryBundle
| └ ... copy all ...
to store a category at a timesheet, set header FORM-CATEGORY at POST /api/timesheets or PUT /api/timesheets/$id requests
//timesheet response
{
"activity": 1,
"project": 1,
"category": "holiday"
}