Network models and latency support

[jordi]

Add the latency support, to enable some cost per connection between nodes.

Some possible network models to be supported are the followings:

• Pajek
• GT-ITM
• King
• Skitter
• Rocket-Fuel
• Mercator

This should be directed to:

• Build a new hotspot LatencyModel?, to save whole connection costs information.
• Build a new hotspot LatencyParser?, to enable parsing from different formats and to load them to the LatencyModel?.
• Implement a LatencyModel?
• Implement the different parsers for each latency model (Pajek and so on).

Some examples exists on sourceforge (collaborations):

• Marcel's and Tomas' works support Pajek formats.
• Thomas' work supports BRITE and GML formats.