getData
Get an instance's data from localstorage.
    connection.getData(params)
  
  Looks in localstorage for the requested instance.
Parameters
- params 
{Object}:An object that should have the [conenction.id] of the element being retrieved.
 
Returns
 {Promise}: 
A promise that resolves to the item if the memory cache has this item. If localstorage does not have this item, it rejects the promise.