Refactoring: reduce code duplication in METIS sim

Put the common code for the multiple path loss models in a function.
Print the statistics only of the 64 central rooms

Print the statistics only of the 64 central rooms instead of all rooms
to remove border effect.
Use draw() instead of show() in AccessPoint plot
Improve module docstring
plot_all_rooms now return the used matplotlib axes
Remove initial _ in _simulate_for_a_given_ap_assoc
Small cosmetic changes
Add METIS simulator that disable APs without users
Calculate the capacity of each user

The METIS simulator now also calculate the capacity of each user in
addition to SINR.
Fix small bug in capacity calculation
Fix bug: plotting APs with decimation != 1
Fix errors caused by changes in 29cd4f40ef84f68847

Commit 29cd4f40ef84f68847d2713294774e0bfe22901b made changed in
simulate_metis_scenario.py that broke the "METIS Simple Scenario.ipynb"
notebook and thus we are fixing this here.
Improve python3 compatibility: Add some parenthesis

Add parenthesis to some print statements to improve python3
compatibility.
First version of the AP association IPython notebook
METIS2: Show extra info when a point is clicked

Show extra information in the plot when either an access point or an
user is clicked.
Improve code quality and fix python3 plot bug

For the ap_colors numpy array used in the plot we now use a 'U4' dtype
instead of 'S4'. This make it compatible with both python2 and python3
at the same time.
Plot interactivity: select AP or users

When an AP is selected, the color of the users associated with it change
to green. When an user is selected a small circle is show in the AP that
the user is associated with.
Change the color of the selected user in the plot
Change the color of the selected user siblings

When a user is selected its color is changed to cyan. Now the color of
its siblings will also change, but to green.
Small changes to conform with pep8