Add new method for objective function: Clique

The new method to compute the objective function uses the distance
between all pairs of areas in a region.
Makes use of numpy's linalg.norm.
Change from SquaredEuclidean to Euclidean

The experiment is outlined using the Euclidean distance.
Exact algorithm for P-regions added
Update P-regions algorithm: with and without Cutting Planes
Exact algorithms for min-p added
Added changes for P-regions exact
Heuristic Concentration test added
HC changes
Update
Revert bad decision on conflict
Set number of cores to size of processes pool

Also changed the way that the random received the seed.
Before the problem was that when using the same 'session' or
script, the process ID was used as seed, giving the same result for the
randoms.

Added test to ensure that we get different results from the same
execution.
This should fix #17
Need to confirm that also is good for #16
Try to import gurobipy

This is a very particular import. It is not necessary to use the other
features of ClusterPy. This is part of #19

 * Should show warning message or something telling the user that a
 certain algorithm is not available.
Fix rimaps and statistics import

Added spaces to help readability
Fix some import issues

Not having some optional modules was raising some import errors with
other modules.
Add version alias

Simply give a way to check for the version.
Related to #15
Some imports related to rimaps now are inside try

Since rimaps and some other related functions require the optional
library Polygon2, the regular user of the clustering methods would
see an error.
Cleanup (imports, a file and spaces)

removed some whitespaces and a couple of unused imports
Add travis ci file

This is a simple Travis file. Next step will be to change it for the
aptitude packages, python-numpy, scipy and matplotlib
Change the version on clusterpy __init__ file

This is one more step on getting #15 done. We'll start update this
number as the version
Fix travis file to install requirements

some pip options require an argument, now the test should install
all the requirements for the version used.