Complete FTP functions mainly.

1. Added sub local_files, target_folder, ftp_exists, ftp_isfile,
ftp_isdir, ftp_file_dir_exists,
check_established_session_and_ask_continue and Upload();
Changed ftpobj to private format _ftpobj;
Added more check in Download().
2. Simplify Download flow and complete Upload flow in RemoteExcelMgt.pl.
3. Add print control options to lib\BC_Term_Menus.pm.
4. Perltidy for t\bc_netadmin_test01.pl, lib\BC_Term_Menus.pm,
lib\BC_NetworkAdmin.pm and RemoteExcelMgt.pl.