Update DebianSecurity&Updates.sh

- Fixed syntax on tar command
- added mysql_secure_installation script
- added "-s" flag for server installs
- added warning against installing OpenVAS on a server
- added Google's backup DNS server(8.8.4.4) and Level3's Public DNS address(4.2.2.2)
- automated SSH config modification
- additional comments
- Made Nikto Executable