Aded Data Helper and Session Helper

These are two objects I find myself using a lot. I feel like the Class Name "Data" might be a bit too generic and would advise an alternate name, nothing came to mind right away.
hmm, i see... `setVar` is the reverse of `getVar`. alright.

i think `isset` should be replaced with `array_key_exists`, in case `$default` is not `null`.