Advanced tests configuration

[mlewand]

Overview

We should introduce advanced tests configuration.

Create Mapping For Test Groups

Developer should be able to easily set WCAG2 A, WCAG AA or WCAG AAA tests without knowing what tests belongs to which group.

e.g.

config.a11ychecker_preset = 'WCAG2AA'

Allow To Exclude/Include Some Tests

It should be possible to add/remove particular tests.

config.a11ychecker_preset = 'WCAG2AA'
config.a11ychecker_include = [ 'foo', 'bar' ];
config.a11ychecker_exclude = [ 'baz' ];