Animation Timeline UI Improvements

[mrtripie]

• Fixed link cel indicator color having no saturation

• Fixed animation tags position

• Restructured AnimationTimeline scene a bit

  • Node tree is organized closer to the way it looks like it should be (IE: The Layer Buttons and Opacity slider are kept inside the same VBoxContainer, all inside the panel container)
  • Renamed things for consistency:
    • LayersContainer/layers_container -> LayerVBox/layer_vbox
    • FrameIDs/frame_ids -> FrameHBox/frame_hbox
    • FramesContainer/frames_container -> CelVBox/cel_vbox
    • Variables in code of CelVbox's children -> cel_hbox

• Improved scrolling

  • Horizontal scrolling is only for frames. Added a FrameScrollContainer script for that.
  • The Animation buttons are now in their own scrollcontianer (sharing the hidden scrollbar theme of the tag scrollbar)

• Automatic minimum size for timeline

• Resizable Layer Buttons

  • Made the default size for Layer Buttons a little smaller
  • Layer and cel size is saved between sessions

• Playing animations or adding frames automatically ensures the frame button is visible

• Combined _on_AddLayer_pressed and _on_AddGroup_pressed into 1 add_layer method

• Removed some hacks

• Added some hacks

  • Ensuring the frame is visible when adding frames requires 3 call_deferred calls chained together...

[OverloadedOrama]

Looks amazing, thank you!