* Add dockable container plugin
Experimenting with it, also added a tabs_visible property to the DockableContainer. Removed some code about Tallscreen from Main.gd, but not all of it.
* Add a panel behind the UI, temporarily restore the dark theme
* Remove tallscreen code
* Add edit mode, toggles DockableContainer's tab visibility on and off
* Split tool options into color pickers, left and right tool options
* Remove alternate_transparent_background
* Re-order tool buttons on resize
* Clip content in timeline
* Changes to the tool panel
* Removed some old unused node variables
* Restore Zen mode
* Set tabs_visible = false by default
* Better way to set tabs_visible = false by default
* Added the license of godot-dockable-container
* Remove unneeded lines
* Update README.md
* Restore window transparency with the canvas
It makes all of the TabContainers transparent however, which may not be what we actually want.
* Change tab names of the UI elements
* Remove unneeded nodes from ColorPickers.tscn
* Update default.tres
* Let the user hide elements individually
* Add some checks in HandleThemes
* Center tool icons
* Remove unneeded custom panel in SplashDialog
* Bump version to v0.10-dev and some other minor changes
* Fix crash on Zen Mode
* Added a hacky way to fix the issue with the palette panel size
