Tulip 3.8.0

This release contains a new import plugin for the GEXF file format and a new "edge weighted" version of the "Depth" metric plugin.
The Python bindings and Python script view have been greatly improved. Especially, a new module called tulipgui has been added to allow the management of Node link diagram views. The auto-completion system is now case-sensitive and the plugins developped through the Python script view are saved in the graph tlp file for further reloading.
Two new rendering parameters have been added in the Node link diagram view Editor. These allow to enable the "billboarding" of the nodes/edges labels and to keep the same 3D camera point of view when navigating through a hierarchy of subgraphs.
Some performance improvements have been achieved in the Tulip core library about the management of edges and the hierarchy of subgraphs.
Many bugs were also fixed in the Tulip plugins and GUI.