Added wxRichToolTip class.

Added wxRichToolTip class.

It can be used to show more customizable tooltips than the native wxToolTip
but at the price of using generic implementation in some cases (actually
almost always now, with the exceptions of text control tooltips under MSW).

Extra features include:
 - The balloon-like tooltip form.
 - Possibility to show an icon.
 - Title display in a different form.

More customization could be added later. It should be also possible to fully
implement this class natively under MSW.

Update the dialogs sample to show the rich tooltips in action.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69463 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775