Added the test to verify title on /explore

Added the test_explore_title to address #48
So the problem here is that you are comparing text with an element on the explore page- which doesn't exist. There is nothing called "page_title" on explore.py. It would be better to do "Assert.equal('Explore - Mozilla Webmaker', explore_page._is_page_title_visible)", as that would compare the title with the text returned by the method.