Better handling of phantom page.open

page.open is asynchronous and has a callback to know when the page is opened.
Thanks to that it's possible to better control the page opening and provide more clear messages when something fails.
1.2.1
Refactor attester as a module

Make attester as a module that can be used by other node modules and not only a command line tool.

Responsibilities are split in different submodules that communicate through an event bus that allows a greater extensibility.