Store canvas attributes in the canvas itself in the dialogs sample.

Store canvas attributes in the canvas itself in the dialogs sample.

Simplify the code by not transferring font and colours between canvas and
wxTheApp but use canvas font and colours directly instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62265 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775