change the icon of edit button in connection dialog

this icon is to start editing the little code editor below.

since the icon is {} it is difficult to interpret that way.

i think it'd be better to make it a pencil icon which is more common for "edit" button. (or, i'm not even sure if this icon is really necessary in the first place; users might want to just click on the editor at the bottom itself to start editing the code, which is more intuitive.)

also, the icon should be closer to the little editor so that it becomes clearer that this botton is related to it.