Linked Cel Refactor and Timeline Refactor Tweaks

[mrtripie]

Implemented #719

• New concept of a "link set":
  • Layer's linked_cels array of Frames was replaced with a cel_link_sets array of array of Cels
    • Each inner array represents a "link set", allowing for a single layer to have multiple different sets of linked cels
    • The Frames were changed to Cels which makes certain things easier and others harder, but I think makes more sense
  • Each Cel has a reference to its link_set array, if linked, or null if not
  • The linked cel indicator on Cel Buttons is now a different hue depending on the index of the Cel's link_set inside the Layer's cel_link_sets array.
    • An issue with this is that when a link sets are added/removed to cel_link_sets, other link_set's hue will change. (and when undoing and its removed/added back it will likely be a different color than before)
      • If it seems worth it, this could be solved by representing link sets with a simple class or Dictionary containing an Array and hue float, and setting automatically the hue of the link set when its created.
• Linked Cel data was moved from PixelLayer to BaseLayer to make it simpler for multiple layer types
• Deleted Project.duplicate_layers()
• Enabled drag and drop to move/swap linked cels on the same layer
• Can now link/unlink multiple cels at a time
• Enabling new_cels_linked no longer links the current frame's Cel
• When new_cels_linked is enabled, new Cels will be linked to previous frame's Cel (the Cel to the left of the new one)
• Updated the tooltip for PixelLayerButton's LinkButton to be more accurate (it doesn't enable/disable Cel linking, it enables/disables automatic linking of new Cels when creating a new frame)

Timeline Refactor Tweaks:

• Rewrote the copy methods on BaseLayer to use get/set_content, as they now should work on any layer type (without overriding) and are only used in one place, removed the methods and inlined where used)
• Added a texture argument to set_content

Other:

• Bug fixes from my timeline refactor
• General cleanup

[OverloadedOrama]

Is this string used somewhere? Shouldn't this be "Link Cels to"?

[mrtripie]

Its inside the right click menu on cel buttons.

[mrtripie]

Actually, it seems like this got messed up somehow, I'll update it in a minute

[mrtripie]

Should be fixed now

[OverloadedOrama]

Looks good to me. I tested it too and couldn't find any issues, so it should be good to merge. Thank you!