further removal of magic numbers and more constants

...ncontrol/tangostationcontrol/clients/attribute_wrapper.py

...ncontrol/tangostationcontrol/clients/statistics/client.py

...tationcontrol/tangostationcontrol/clients/udp_receiver.py

tangostationcontrol/tangostationcontrol/common/constants.py

...tationcontrol/tangostationcontrol/devices/antennafield.py

...stationcontrol/tangostationcontrol/devices/beam_device.py

...stationcontrol/tangostationcontrol/devices/sdp/beamlet.py

tangostationcontrol/tangostationcontrol/devices/sdp/bst.py

...ioncontrol/tangostationcontrol/devices/sdp/digitalbeam.py

tangostationcontrol/tangostationcontrol/devices/sdp/sdp.py

tangostationcontrol/tangostationcontrol/devices/sdp/sst.py

tangostationcontrol/tangostationcontrol/devices/sdp/xst.py

tangostationcontrol/tangostationcontrol/devices/tilebeam.py