Register relative counter value

DBC-1603

A type added to the counters (Relative/Continous) !image-2021-12-24-11-36-04-541.png|width=809,height=116!

Continuous counters work as it was before the change - when the new reading is registered - the user must enter a value the same or higher than the last reading.

Relative counters - when the user is registering the reading - only registered values must be entered. The system will calculate automatically the current value on the counter.

Migrate counters and measurements wizard in Assisted Setup - template updated with a field to specify the type of the counter. **