Add FTP Support

[Sarafian]

With dependency to PSFTP.

With FTP support we could download ftp://ftphost.com/Folder1/File1.zip with something like this

something = @{
        DependencyType = 'FTP'
        Host = 'ftphost.com'
        Path='Folder1/File1.zip'
        Username='username' #Optional for annonymous
        Password='password'
        CredentialExpression='' #Something that returns a PSCredential object
    }