add support for global meshes for TELEMAC system

Global meshes have the particularity of being closed meshes, with triangles crossing over the 180/-180 dateline. To be able to add support for global meshes throughout the TELEMAC system, certain routines need revision/adaptation.

For example, here are the boundaries detected by the modified pretel/extract_contour.py routine:

As requested by @boris.basic in !176 (closed), find below the following steps for implementing support for global meshes in the TELEMAC system.

• pre-processing (PYTHON/PRETEL) for boundaries.
• adapt routines for TOMAWAC
• adapt routines for TELEMAC3D
• (eventually) adapt routines for other openTELEMAC modules or features (GAIA, WAQTEL, GOTM, AED and coupling).
• add test case (see comments)