[feat] /services implementation

[lgrd]

Need

We need to know available services, and to manage them.

Tasks

• [x] GET /services. See #43
• [ ] POST /services
• [x] GET /services/{service}. See #49
• [ ] PATCH /services/{service}
• [ ] DELETE /services/{service}
• [x] GET /services/{service}/restart. See #45