VPN autoconnect/always up logic improvement

Windows and FortiClient VPN login controls are now more logically positioned and coordinated. Connecting to a VPN tunnel that requires a certificate is a one-step process. If a tunnel requires a certificate, the user selects the certificate from the Windows login screen, in the same form where they provide VPN credentials. This is similar to connecting to VPN from the FortiClient GUI. This improvement eliminates an additional dialog that appeared for certificate selection in 7.0, streamlining the process for end users.