Adding a tree of animations and directions to the sprite editor.
Sprite editor: attempt to fix sudden resizes when moving the splitter.
Sprite editor: resizing is now okay.
Sprite editor: add a checkbox for loop on frame instead of using -1.
Sprite editor: remove unwanted space when saving.
Sprite editor: give a more appropriate size to the animation panel.
Sprite editor: use a better icon to choose the source image.
Sprite editor: update titles of components when selecting direction.
Sprite editor: disable the loop field too when no animation is selected.
Sprite editor: fix sprite marked as unsaved as soon as you open it.

ChangeEvent of JCheckBox is triggered by setEnabled(), not only when
the use checks/unchecks the box.
Sprite editor: show animations and directions in a tree.
Sprite editor: select the current animation and direction in the tree.
Add more precise info about what has changed in sprite updates.
Sprite editor: show empty sprites or animations as folders when empty.
Sprite editor: initially select the animation if no direction is selected.
Sprite editor: show the animation and direction selected in the tree.
Sprite editor: prepare how to update the tree without rebuilding it.
Sprite editor: refect the current selection into the sprite tree.
Sprite editor: select the root node when no animation is selected.
Sprite editor: show the icon of each direction in the tree.