Added global_fragility_vulnerability_2018 of Martins and Silva

Merged Tara Evaz Zadeh requested to merge feature/fragility_functions_Martins_Silva into master

As described in, the fragility and vulnerability files are added to avoid uploading them to the losscalculator repository. Please let me know any issue or inconsistency that you can see.
\approve @ds @cnievas
\rfc @shinde @LaurensJN

Edited by Danijel Schorlemmer

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