add FEFLOEInterface class in FileIO
add FEFLOW2OGS tool
correct a variable name
add FEFLOW import
changed according to comments
fix reading elevation values and set material ID by layer ID
some clean up
add <cctype> to use std::isalpha
fix node-ordering of imported prism and hex elements
Merge pull request #410 from norihiro-w/add-feflow-import

Add FEFLOW import