sessionmanager: adds empty client script to enable client to server remote callbacks

[bladecoding]

This fixes the case where callbacks weren't working sent from the client to the server. For example

client.lua

TriggerServerEvent("callbackTest", function(val)
  Citizen.Trace(val) --would never get called
end)

server.lua

RegisterNetEvent('callbackTest')
AddEventHandler('callbackTest', function(cb)
  cb("test")
end)