Code improvement in convert.py

improve code reading and clarity of topology parser:
*modify the connections binding
=>def fiber_dest_from_source to find all dest_city connected to a source_city
=>def fiber_link to return the fiber link from source_city to dest_city
*makes the parser algorithm more understandable
*prepare for the equipment parser

Signed-off-by: Jean-Luc Auge <jeanluc.auge@orange.com>

gnpy/core/network.py

@@ -13,7 +13,6 @@ from networkx import DiGraph
 from gnpy.core import elements
 from gnpy.core.elements import Fiber, Edfa, Transceiver, Roadm
 from gnpy.core.units import UNITS
-from gnpy.core.equipment import *
 
 
 MAX_SPAN_LENGTH = 125000