Libgda's minimum required version

[Vivien Malerba <vmalerba gmail com>]

Hi!

Libgda is an external dependency and I would like to propose to
recommend version 4.0.7 instead of the currently recommended version
4.0.0:
* there is no API/ABI change between the 2 versions
* many bugs have been corrected

Please let me know if/when I can update the External Dependencies of
GNOME 2.29.x page and the jhbuild's 2.30 moduleset file.

Regards,

Vivien