Rename informant submodule to core

This should help avoid confusion when referring to the 'informant'
folder (e.g. see README.md).
Switch back to Firefox for WebDriver tests

Seeing sporadic failures when using PhantomJS driver, see
ghostdriver issue #140.
Update to use new shaded artifact name
Travis-ci upload informant.jar to fixed location

And update README.md link to point to this fixed location.
Display commit hash for SNAPSHOT versions
Do not use underscore prefix on non-private field

Angular is logging info message about this:

'Referencing private fields in Angular expressions is disallowed!'
Clean up Firefox warning