Changelog:

Following are changes made to extend SWANS with
(1) multiple interface support
(2) collecting statistics on radio modes (for calculation of wasted energy)

***********************************
**** multiple interface support: **
***********************************
* Added field Field.mapPrimaryRadioToSecondary to Field class which maps between 
primary and secondary radios. Used in multi-radio support to move all radios
when the primary radio moves. Primary radio is the one on which 
Field.startMobility() method is invoked. (Field.java)

* Added method Field.addRadio(...) that accepts, in addition to other 
parameters, also id of the primary radio. This method should be invoked when
a secondary radio is added to the field. (Field.java)

* Changed method Field.moveRadio(...) to move secondary radios when
the primary one is moved on the field (Field.java)

* Changed method Field.delRadio(...) to remove mapping to secondary radios
when the primary radio is removed (the secondary radios are not removed 
from the field) (Field.java)

* Added field RadioInfoShared.name to indicate the name of 
the radio (BT, WiFi, etc.). It is used to resolve the interference issue --
the interference occurs only for radios sharing the same name (see below). 
(RadioInfo.java)

* Added method RadioInfoShared.getName() to retrieve the name of the radio
(RadioInfo.java)

* Added method RadioInfo.createShared(...) that accepts also the name of the 
radio (RadioInfo.java)

* Changed method 
Field.transmitVisitor.new SpatialTransmitVisitor() {...}.computeSignal(...)
to prevent interference (and locking on a signal) between two radios with 
different names (Field.java)

******************************
**** collecting statistics: **
******************************
* Added class jist.swans.radio.RadioModeStats for collecting statistics on 
times a radio remains in each of its modes (sleep / idle / transmit / receive / 
sense), and calculating wasted energy.

* Added method RadioNoise.setStats(...) that accepts RadioModeStats as a 
parameter (RadioNoise.java)

* Changed method RadioNoise.setMode(...) that notifies statistics collector
on the change of radio mode (if such collector was set for the radio) 
(RadioNoise.java)

* Added field RadioInfo.stats to hold statistics collector (RadioInfo.java)

* Added method RadioInfo.getStats() to retrieve statistics (RadioInfo.java)

* Added method Field.RadioData.getStats() to retrieve statistics (Field.java)

Note: access radio statistics collector from Field instance by radio id as: 
field.getRadioData(id).getStats()