test speedup of different Java map implementations

[jordi]

Given the notes by Max, there is almost a speedup of 1.5 when using Hashmap instead of TreeMap?. Notice that TreeMap? was initially selected becouse:

1. Ensures operations cost in O(log).
2. It retrieves the stored pairs in incremental order.

Goal: Test different Java map implementations.

Expected tasks to do:

1. Speedup analysis of different Java map implementations.
2. Select and modify the default NetworkImpl? map with the fastest one.
3. Modify the NetworkImpl? iterator in order to retrieve nodes in incremental order of its Ids.