New functionality to provide a sitemap_index.xml file for accounts with more than one microsite.
Additionally this fixes several bugs in shopserve:
- Unpublished sites were still being served.
- Fix for SCSS includes on relative paths in themes when operating in developer mode.
- Crash when converting string to array in liquid.
- Crash when converting bool to array in liquid.
- Crash when slice filter first index is out of bounds in liquid.