fix(phantomjs): fix server port never passed to phantomjs script

If the server port was changed through the `PORT` environment variable
the phantomjs failed due to a hardcoded port in the script.
docs(pages): update documentation with new bin options
feat($core): add support for SlimerJS

Using the `slimerjs` option, it's now possible to run test in SlimerJS
as it's done with PhantomJS. A server is started and the slimerjs script
will access the test page and report the result in the terminal.

The --slimerjs-bin option allow to change the path to the SlimerJS excutable.
fix(browser): fix hidden errors when the parent group already had success