Allow specifying password to skip dialog

[rickparrish]

My RDP/VNC client allows storing passwords, so I've modified VncSharp to accept a password as a SecureString, which then allows my client to skip the password prompt dialog for VNC connections.

It would be great if this could be merged -- will make things easier for me to merge future updates to VncSharp, and maybe it would be useful to someone else as well.

[kmscode]

In order to prevent a "breaking change" I would recommend leaving public static string GetPassword() as is, and create a new ublic static SecureString GetPassword() accordingly. This way any existing consuming applications can still function, but you can also get the benefits of SecureString. Hopefully other apps would update accordingly to use the new method going forward.