Breaking changes to --nofx and --save_stats options

Hi,

this pull request make breaking changes to the behaviour of some options:
* Change default to "do not show the pages in the browser", change the option
--nofx to --fx to show the pages;
* Change default behavious for --save_stats from "ask the user" to "do not
save" the stats, --save_stats option still saves them.

Cristian