Follow chezmoiignore for post-chezmoi scripts

[ledif]

The post-chezmoi scripts in .chezmoiscripts (run_after_01-xfconf-profile.sh, run_after_02-xfce4-panel-profile.sh, run_after_03-wallpapers.sh) will end up modifying user files which the user might want to exclude updates for.

For example, run_after_03-wallpapers.sh will end up modifying properties in ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml. We should check in that script if that xfconf XML file is not in the user's chezmoiignore file.