Mainly adjust BC_NetworkAdmin's new method, ftpobj and ftp_login.

1. Adjust BC_NetworkAdmin's new, ftpobj, ftp_login.
2. Add constants for FTP.
3. Add clear_screen switch to BC_Term_Menus->prt_control hash.
4. And code to RemoteExcelMgt.pl, in order to reuse established ftp
session. Be very conveniency now :)
5. Add few print code to t\bc_netadmin_test01.pl