Embed SVG data of the wx logo into the library itself to make it
available to all wx programs, including the samples. This is a bit
wasteful, but <12KiB is not really noticeable compared to the library
size.
In webview sample toolbar use wxBitmapBundles created from SVG files
instead of XPM bitmaps, as this results in much better appearance in
high DPI.
Closes#2642.