Change Level export to have a text box for target filename

[scallyw4g]

Currently, there's a hard-coded destination filename of 'test.level' when you click the "Export Level" button. It would be nice if you could input a destination filename in the same way that you can name a brush using the "BrushName" text box in the "Brush Settings" window.

I would suggest having a char CurrentLevelName[NameBuf_Len] buffer .. somewhere.. that represents the current level name and the destination filename.