Change error page

https://github.com/OpenDataServices/lib-cove-web-2/blob/main/libcoveweb2/views.py#L156

"Sorry, there was an error." -> "Internal Server Error"

https://github.com/OpenDataServices/lib-cove-web-2/blob/main/libcoveweb2/templates/libcoveweb2/error.html#L5

Change warning to red colour

Request from @Bjwebb