Import Dialog

[iimog]

Improve the user experience when importing carts. The user should see a loading animation, that ends when the import has finished.
For that purpose all sync actions have to promise to deferred. This means major changes to the sync action and passing it down through each method that calls it (addItem, addCart, updateItem, importMetadata, ...)

After import has finished the user should get a summary (carts imported, features imported, annotations imported, any errors, ...)