Stamp saving and opening now works

Yay. The file format ("*.stamps", something I invented) is a simple
text-based format that anyone with a text editor can understand and mess
around with.
Add a stamp name editor, and various bugfixes

Stamp name editor now exists but doesn't work yet. A few bugs fixed,
too.
Allow stamp name editing

Now you can change stamp names. Final thing to do is to get the text to
wrap and elide properly.
Fix a bug

Should really have been range(3). That being said, the zip isn't really
needed in the first place, so it can go away. The bug caused tiles on
layer 2 to paste weirdly.
Improve stamps

They work better now. Not very well, but better than before. Still
buggy. :( But less buggy.
Change default zone position

New zones are now created at (256, 256) instead of (16, 16). I've been
planning to do this forever, but Zementblock mentioned it and I decided
to do it now. :)