This lets us create ValueSlider and CollapsibleContainer nodes properly via the add node button, instead of instancing their scenes. They have also become more a bit more themeable. Eventually, ValueSlider.tscn and CollapsibleContainer.tscn will be deleted.
* Remove animation tab from the export dialog, unify it with the first tab
* Tidy up the UI using GridContainers
* Make ExportDialog a ConfirmationDialog and clean some code
* Make project a parameter in export methods
This will be useful in the future for exporting multiple projects at once via terminal arguments
* Add a layers option in the export dialog
Currently only visible layers and selected layers, need to add specific layer selection and handle group blending properly.
* Align everything to the left
* Change "directory" into "folder"
* Make animation direction affect spritesheets and multiple png exporting
Besides just gifs and apngs
* Minor code re-organization
* Keep spritesheet options when changing tab
* Use the Unicode multiplication sign in the dimension label
* Specific layer exporting with group blending support
* Change file format cursor mode to pointing hand instead of forbidden
* Add a new custom CollapsibleContainer node and use it for advanced settings in the export dialog
* Change Popups node into Control so its children will automatically inherit the theme
* Add the TextureRect of the CollapsibleContainer in the UIButtons group
* Update ExportDialog.gd
* Disable "Create new folder for each frame tag" when gif/apng is selected, and hide it completely on the spritesheet tab
* Fix "Create new folder for each frame tag" being visible even if the CollapsibleContainer's button is not pressed
* Show layer path for each layer in the export dialog's "Layers" option
* Update translations
* Update strings
