Features and Bugfixes

fixed bug in extension MDI.
added methods menuCreate and menuConfig to extension MenuBar
fixed bug in base class PluginJobs
got rid of Module::Load::Conditional;
added method getFileIcon to extension Art
extension art now has a cache to reduce system resources for frequently used icons.
corrected documentation in extension Panels
extension MDI now has a dropdown item for recent files on the toolbar
revised about box in extension Help