Caused in CreateNewImage.gd, Global.current_layer = 0 should be under Global.canvas gets set to a new canvas, and after its _ready() method gets executed. The crash occurred when a layer above 0 had transparency less than 100, and a new image was created. _on_OpacitySlider_value_changed() in AnimationTimeline.gd was executed on the old canvas right before it was destroyed, while Global.layers had been cleared.
Also removed _on_OpacitySlider_value_changed() from Main.gd, it served no purpose there.
* Sync fork
* Added 'Lock aspect ratio' when creating a new image
* Added common templates in 'CreateNewImage' dialog
* Last fix
* Added translation strings
