Changed Version to add tracker version separately

- Tracker version is separate from the gradle version
  We avoid populating it this way and we still keep the same format for
  both systems (gradle & tracker)
Added a few more toString checks

To make sure all kv-values are strings
Loggging for TrackerPayload
Comments to SchemaPayload
Added new format for POST request URIs
Fixed potential bugs with Payload classes

- Using the ObjectMapper we stringify every kv-value in the Payload
  classes