new tool "checkMesh"

I propose a command line tool "checkMesh" which shows the information of a mesh. Current implementation outputs basic information such as the numbers of nodes and elements, bounding box, material IDs. In the future, we may want to include validation of a mesh as optional.

Maybe you could use ```readMeshFromFile()``` from FileIO/readMeshFromFile.{h,cpp}? An alternative would be to substitute the impl. there.