obex: Fix race condition when moving to Downloads dir

Rather than doing g_file_test()s then moving the file.
obex: Fix notifications not working

We passed the original filename sent, instead of a full file path
as saved on disk.
obex: Remove the status icon

The Bluetooth icon will already show up when a transfer is on-going
so we don't need an extra icon showing up in a place where we
wouldn't look.