Removes comma after json message

Caused exception:
net.sf.json.JSONException: Found starting '{' but missing '}' at the end. at character 0 of null

Signed-off-by: Aske Olsson <aske.olsson@switch-gears.dk>
Moves isBuilding and lastJob to Lamps class

The methods do not really belong in PeriodicLampUpdater (AsyncPeriodicWork),
they are better as general methods for the plugin.

Signed-off-by: Aske Olsson <aske.olsson@switch-gears.dk>
Moves updating lamp status to Lamps class

Signed-off-by: Aske Olsson <aske.olsson@switch-gears.dk>