Update of LBE documentation

[prisma34]

Update of lbe.rst and lbe_thermochemical_properties and creation of lbe_contamination.rst in order to complete the API Guide with the lbe-related contamination properties.

[lelaus]

This issue accomplishes the fourth task of issue #187 .

[lelaus]

The review of what added in all the commits here pushed is yet to be done.
API Guide is yet to be updated accordingly.