v1.1.5: fix save corruption on write

Fixed

• Saves written by the editor were rejected as corrupted by the game in
  most cases, due to missing base64 padding in the output file. All
  writes now produce valid files.
• Saves corrupted by previous versions can be repaired: open them with
  v1.1.5 and re-save, no changes needed.

Changed

• Items tab: New Entry replaced with an Add Item dialog (pick any item
  you do not own, plus a count).