Sticker boxes

[Orion Pobursky]

For flat stickers I think:
sticker-back-1-9-x-1-9 is bit excessive but I can live with it.
add an optional qualifier like "r" for rounded corners

Formed I like:
<part number>bNN

Should we have a new folder in p?
Something like p/sticker
If so we'll need a new !LDRAW_ORG type as well. Something like Sticker_Back or Sticker_Box

Note, not all sticker backs need to be subfiled, only the one's that get a lot of reuse.