Very simple cache

This is a extremely simple cache system that leverage in [flask-cache](http://pythonhosted.org/Flask-Cache). 
The approach is cache (memoize) the chunk of html content of each page,  and delete it after an edition. 

Would be great to cache the whole page (e.g. decorating `@cache.cached()` the view `display`) but this approach would have the problem of the dynamic "flash" success message, that will be shown in any further request.