Implement channel summation for partial ring arrays

[zieglerad]

Currently in KTChannelAggregator it is possible to perform channel summations for ring arrays for arbitrary numbers of antennas in the ring. However the antennas are always spaced around the ring circumference with an even separation of 360/N degrees.

Request: Extend KTChannelAggregator to sum the signals from partial ring arrays. For example N antennas in a quarter circle. One way I can imagine implementing this is to change the parameter responsible for placing the antennas at the appropriate angular positions from 360/N to theta/N where theta can be user specified. E.g. theta=90 would be a quarter array, theta=180 would be a half-circle array.

It would also be useful to be able to define the starting angle for the array population since different symmetries exist depending on if there is an antenna in the partial array located at theta=0 or if the first antenna is located at theta/2N.

[psurukuc]

Still needs testing based on a real egg file