[AsYlum-]

Port of #143 by @DatMoshu onto current master, with fixes. Supersedes #143.

• Animations > Export Animation > Pack Frames to Sheet: packs the chosen directions of an action, or all actions of the body, into anim_{body}_{action}.png + .json (frame rect and center) + _guide.png. Options: max sheet width, spacing, one row per direction.
• Directions 5-7 can be packed too (off by default); on import they are flipped back into 3-1, unless the sheet also holds the stored direction.
• Animations > Import Animation: unpack one sheet into the selected action, or bulk-import every anim_{body}_{action}.json of the selected body from a folder. Replace or append; MUL bodies only.
• Items > Misc > Export Range to Sheet / Import from Sheet: same for item ranges (decimal or hex, up to 1024 items).
• Sheet dialogs remember the last folder for the session, starting in the output path.

Changes from #143:

• Append no longer recolors existing frames (palette is fitted, not replaced); black stays visible instead of turning transparent.
• UOP bodies are refused (no UOP animation writer on master); directions 5-7 are un-flipped into 3-1 instead of dropped.
• Export all works on collapsed bodies; Cancel no longer reports success; bad or partial sheets change nothing and are reported.
• Item import checks id range and MUL size, updates the list and detail view.
• Guide marks each frame's real anchor. AlphaSorter/GraphicSorter stay where they were; dialogs are regular designer forms.
• JSON shape is unchanged, so sheets made with Animation Frame Packer and Unpacking.  #143 still import.