General UI Improvements (0.25.1 Alpha)

This update brings a number of small usability and aesthetic improvements to the GUI.  Most prominent is the tool chooser dialog, large portions of which were re-written.  It's more consistent in appearance, the currently selected tool should always be highlighted when the dialog box comes up, the paint tools load their color into the color picker when the dialog comes up and the scroll bars scroll much faster now when the mouse wheel is used.