Improve Top div layout and fix #34

Changes add a new parameter "data-period" to Top div to show only
a selected period of the JSON file. Also fix the #34 and now it is
possible to place several Top divs and all of them are replaced.
The layout used for the table is bootstrap-ish.
Rebase to master this branch
Merge branch 'period-top-people' of github.com:VizGrimoire/VizGrimoireJS-lib into period-top-people

Conflicts:
	src/Viz.js