Auxiliary functions that should be available for all commands

[luizaandrade]

This should be a new do-file (not ado) to be saved in iefieldkit/src/ado_files/iefieldkit_aux.do. It should contain functions to perform the following tasks:

• Test that a file extension was specified in a filename
• Check that a folder exists

[DenisseO]

Working on #201