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.
Trying to merge layers into the timeline, and eventually add more features like "share layer with all frames", among others. THIS IS NOT FINISHED, IT WILL *NOT* WORK PROPERLY. Once it is finished, this branch will be merged onto master.
So far only add layer and add frame work, and even they may have some issues. Undoing also does not work properly yet.
The UI is also not finished, as it currently has problems with the scroll containers.
For example, if you hover over the "English" button while the language is Greek, the hint tooltip will be "Αγγλικά", which is the Greek word for English.
To avoid issues with the TreeItem strings being translated. Starting to get more translation-friendly again, will commit changes to Translations.pot, en.po and el.po soon.
