Unxfailed test_that_checks_the_tabs() and updated the test logic according to the comments in Bug 824471 - New Personas tab on mobile site not working as expected

Added a new page object for themes page, for now this is used only as a return for clicking on the themes tab
Update after review. Removed init method from themes page object.
Merge pull request #692 from chirarobert/update_test_that_checks_the_tabs

Unxfailed test_that_checks_the_tabs() and updated the test logic accordi...
Removed reference to Pivotal Tracker.
Merge pull request #693 from mediocrity/remove_pivotal_reference

Removed reference to Pivotal Tracker.
Xfailing failing tests on amo.dev
Merge pull request #694 from AndreiH/xfail_tests

Xfailing failing tests on amo.dev
Unxfail tests as Bug 979838 is resolved
Merge pull request #695 from mozilla/unxfail_addon_tests

Unxfail tests as Bug 979838 is resolved
"What's this?" missing from "Memchaser" app under Version Information
Merge pull request #696 from AndreiH/bug_919417

"What's this?" missing from "Memchaser" app under Version Information
Unxfailed sorting tests because they are xpassing.
Merge pull request #699 from chirarobert/unxfail_test_search

Unxfailed sorting tests because they are xpassing.
Fix "test_the_logout_link_for_logged_in_users" on stage
Merge pull request #701 from AndreiH/fix_stage

Fix "test_the_logout_link_for_logged_in_users" on stage and olympia