Add support for global meshes

for pretel:

• added support for global meshes in extract_contour.py (bug for triangles crossing the -180/180 line)
• added 2 functions in utils.geometry to optimise generate_atm (now more than 50 times faster)

for partel:

• added reinitialisation for IRAND (feature to be tested before merged, this is a sensitive implementation IMO). Parallel computation is running fine - for a few examples tested - using this implementation. Although results were not checked.

more info on the forum post