Return service location only for Windows clients >= 1.6

- [x] Implement sending client version to core
- [x] Filter out service locations for clients that are older than 1.6
- [x] Implement checking client OS
- [x] Implement sending client OS to core
- [x] Filter out service locations for clients on other platforms than Windows
- [ ] ~~(optionally) persist client OS and version information in the database~~ <- not planned currently