Handed services' unregister when board is disconnected

Jira Issue: WP-1125
Fixed wrong conversion of values read from sensors

Jira Issue: WP-1125
Fixed bug which prevents to register several sensor of same type

Jira issue: WP-1125
Merge pull request #6 from glatorre/WP-1125

Handled services' unregister when sensors/actuators have been removed