added constants.py and replaced most magic numbers

Closes L2SS-954

tangostationcontrol/tangostationcontrol/beam/hba_tile.py

 import numpy
 from math import sin, cos
 
-# Number of antenna dipoles in each HBA tile
-NUMBER_OF_ELEMENTS_PER_TILE = 16
-
 class HBATAntennaOffsets(object):
     """
         This class helps calculate the absolute offsets of the antennas within a tile,