[GTK][Jhbuild] Move ATK to the main moduleset, bump ATK, at-spi2-(atk|core) versions to 2.8.0
https://bugs.webkit.org/show_bug.cgi?id=113883

Reviewed by Martin Robinson.

* gtk/jhbuild-optional.modules: Remove the ATK entry as it is now placed in jhbuild.modules.
* gtk/jhbuild.modules: Add ATK to the list of webkitgtk-testing-dependencies metamodule, using the 2.8.0 version.
The at-spi2-core and at-spi2-atk versions are also increased to 2.8.0.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147574 268f45cc-cd09-0410-ab3c-d52691b4dbfc