Flag for skipping properties equal to default

[joente]

Sometimes you might want to ask for properties, only when they aren't equal to the defined default value.

Maybe add a new flag, which tells ThingsDB to look for the thing which is wrapped:

• if the thing is non-typed: just return the property if it complies with the definition (no change).
• if the thing is typed, check if the value is equal to the default value and if so, ignore the key/value pair in the result.