Adde the plugin to show the current logged on user

Closes #29 

Example output:
{
    "loggedon_users":  [
                           {
                               "Session":  "343434",
                               "User":  "Server1\\admin",
                               "Type":  "Local System",
                               "Auth":  "",
                               "StartTime":  "\/Date(-11644473600000)\/"
                           },
                           {
                               "Session":  "434343",
                               "User":  "Server1\\admin",
                               "Type":  "Interactive",
                               "Auth":  "NTLM",
                               "StartTime":  "\/Date(1414555548102)\/"
                           }
                       ]
}