This removes a Dolphin-specific patch to the wxWidgets3 code
for the following reasons:
* Calling wxWindowGTK::DoSetSize on a top-level window can end up
calling wxTopLevelWindowGTK::DoMoveWindow, which triggers an assert
because it is not supposed to be called for a top-level wxWindow.
* We should not be patching the wxWidgets code because that means the
toolbars will still be broken if someone builds without using the
WX that is in our Externals.
Instead, we now use a derived class for wxAuiToolBar and override
DoSetSize() to remove the problematic behaviour to get the same effect
(fixing toolbars) but without changing Externals code and without
causing asserts and other issues.
Using the XPM format for images has become a maintenance problem because
people don't know how to create them. This commit removes all XPM images
and all C files that contain PNG images. DolphinWX now uses the PNGs
in the Resources folder instead, just like DolphinQt and DolphinQt2 do.
