New language related tests

These tests check whether elements in a page inherit language set by either http, lang attribute or meta element, as described in the spec. There is one test for the meta elements part of the spec that checks whether multiple-language values are ignored.  

To test whether language is inherited, the tests use :lang (which is widely supported by major browsers). The tests have built in a ejector seat, which produces a fail result and a message if :lang is not supported by the browser.

HTTP is required for several of the tests. 

One exploratory test (multiple-language values in HTTP header) is omitted here.