Add full-width to the available theme layouts

Make sure to not display the sidebar on full width layouts
Child themes can still turn it on if they desire

see #55
Do not add the parent stylesheet by default

Let child themes enqueue the stylesheet themselves if desired. This will also avoid a potential removal of styles if the legacy mode checkbox is checked by accident

see #61
Set an early priority on the legacy filter thematic_childtheme_style_dependencies

This will ensure any child theme that is using the filter will have it's function execute after and override the parent

see #61