#1173 symbolbox has limited size

[IOhannes m zmölnig]

symbolbox only accepts 38 characters.

this is particularily annoying, as you cannot properly edit the contents of a symbolbox (as in copy/paste, move around to add/delete parts).
so typing e.g. a longish filename (trying to get it right) only to discover that the last 3 characters are swallowed by the gatom is frustrating.

please make the symbolbox of unbound length (like msgboxes).

ideally (and additionally), allow to amend text in symbolboxes.