Here a short update on the UI. The following 4 pictures will roughly show the workflow of sending a file with Swift.
First you right-click on the contact you want to transfer a file to and select "Send File". That item will only be available if the client your contact uses supports Jingle File-Transfer.
A chat view to that contact will appear showing you a chat bubble for the intended transfer. Here you can actually initiate the transfer or cancel it.
After you clicked the send button a input dialog for the description will appear at as soon as you've entered your description the transfer will be negotiated and started.
During the transfer the progress will be shown as a progress bar, like in many other chat applications. The actual presentation could be a bit smoother but this works for starters.