Add Windows Gather SmarterMail Password Extraction post module
Conform to style
Expand path in metasm_shell#file.
Modify prints
Update check_smartermail method

Instead of using exception handling to determine the right path,
the new method simply uses the file? method. It's also renamed as
"get_mail_config_path" to properly describe its functionality.
Be consistent with get_smartermail_creds method's return value
Add support for win shells for file?
Add support for shell session type
Land #2934 - Windows Gather SmarterMail Password Extraction
Land #2937 - Expand path in metasm_shell