* d2ui/skilltree: Don't render availSPLabel
this is handled by the ui_manager now.
* d2ui/custom_widget: Allow them to be cached into static images
* d2player/hero_stats_panel: Remove render() function from game_controls
all ui elements are now grouped into a WidgetGroup, thus rendering is
done by the ui manager.
* d2player/hero_stats_panel: Remove unnecessary widgets from struct
we don't need to store them in the HeroStatsPanel struct anymore as they
are completly handled by the uiManager.
* d2ui/widget_group: Remove priority member
this is already defined by the BaseWidget.
* d2ui/widget: Move uiManager.contains() to the baseWidgets
this method makes more sense on a widget anyways.
* d2ui/widget: Add methods to handle widget hovering
* d2ui/custom_widget: Require define width/height
since the custom render() method can do whatever, we need the user to specify
the width/height such that GetSize() calls are meaningful.
* d2ui/widget: Allow widgets to return the uiManager
* d2player/HUD: Refactor health/mana globe into its own widget
* d2player/hud: Refactor load()
seperate each type of loading into its own method.
* d2player/HUD: Move stamina/exp bar into widgets
* d2player/HUD: Refactor left/right skills into widget
* d2ui/custom_widget: cached custom widgets should use widget.x/y
since we render to an image, we use widget.x/y to position the cached
image.
* d2player/HUD: User cached custom widget for all static images
