This commit turns the icon handling into using a macro so we don't need to do
weird conversions from unsigned long (needed by X11) to uint32_t (needed by
Wayland).
Also simplified the error handling path on Wayland.
This change alters the small square dot cursor to a more visible 16x16
cursor for X11. A new option `spice:largeDotCursor` can be set to use an
alternative 32x32 cursor for the vision impaired.
This brings nanosvg into the project for SVG loading and rendering.
Unfortunatly we can not at this time use a submodule for this project
until https://github.com/memononen/nanosvg/pull/214 is merged.
