Allow minor changes to theme via local.css

A good idea would be to allow users to make minor (or major) changes to the theme, but still let them update the theme pages as normal.

A way to do this is to add "local.css" as a stylesheet into the info file - but not actually have a local.css in the theme.

This way, users can make their custom changes in local.css but these would not be overwritten when the theme is updated and these will also be kept separate making them easier to follow.