it's unused as write_buffer now writes a buffer to the disk.

The previous separation between the fs and ui process wasn't that good. The idea was to have a `ui' process tightly sandboxed, but it was a lie actually. `ui' was one imsg away from making internet connections and accessing data on the disk, so it wasn't really limited in (almost) any way. Furthermore, having to serialize data to/from the fs proc started to become not really maneagable. As a first step to fix this situation, join the fs and ui process.

saves a page to the disk. Also, changes the order of the downloads so the new one is always at the top.

download_lines is a very small value, for a normally sized terminal is exactly 5. This was the cause behind the download pane glitch, 5 was used as *column number* for the reflow. Now, to be honest, the exact width passed to wrap_page is not important. wrap_page will only wrap the size string, which we know is less than or equal to FMT_SCALED_STRSIZE-1 (6). We could also hardcode the value eventually, but using download_cols reads better.