Backend register, class updates

-Backend register fully working, but lacking email verification
-Username and Email getting checked
-Data inserted into nlx_users and nlx_user_meta

-db.class updated
- addToMeta is working now.
- Meta_keys and meta_values can be inserted with multidimensional arrays
- New function added lasterInsertId(), gives back lastinsertedid

-form.class updated
-if placeholder variable is empty it doesn't show placeholder

-user.class updated
-If there's no salt in the constructor a new one is generated.