Scroll to add gateway on action link. Notify user of what is happening

Implements what winnie said: https://github.com/stellar/stellar-client/issues/1006#issuecomment-59303342

Adds scrolling and an alert.

#1006 
But winnie doesn't want it to scroll to the add gateway form. She wants it to scroll to the currencies (since the add gateway form is not necessary since it is already given from the url).