WIP: Add intergrated inkscape extensions manager and Gtk libraries

This merge request adds the directory inkman this contains the extension manager inx and bin py file as well as the supporting module/code that operate the extension plus data in inkman/data/.

It also includes a copy of gtkme, a gobject Gtk based library for making python gtk glade based interfaces very simple. It's kept as a generic library to allow other extension writers to use in the future.

Please review the format of the files, the functionality (on various platforms) and the general sense of the addition. See MR inkscape!2188 (merged) in inkscape master for the other side of this change which includes the menu addition.