Improve display widget Controllers
Extend bgRole API of TaurusController to allow passing the name of a property of the model object as the bgRole.
This allows e.g. to simulate the behaviour of Taurus3 state labels by setting the model to a state and the bgRole to "rvalue":
from taurus.qt.qtgui.application import TaurusApplication
from taurus.qt.qtgui.display import TaurusLabel
import sys
app = TaurusApplication()
w = TaurusLabel()
w.setModel( 'sys/tg_test/1/state')
w.setBgRole('rvalue')
w.show()
sys.exit(app.exec_())
This Fixes #626 (closed) Update: actually, #626 (closed) does not really need this to be closed
Also, fix a related bug with state leds.
Finally, remove the state led of taurusdevicepanels since it is no longer needed.