math/qalculate-gtk: Update to 5.3.0

Add WEBKIT option to use WebKitGTK for display of the user manual in the
application instead opening it in an external browser. Enabled by default
since it's a cleaner way of displaying the docs and webkit2-gtk3 is
needed in the dependency chain for gnuplot anyways.

https://github.com/Qalculate/qalculate-gtk/releases/tag/v5.3.0