Move default site template into solidus

[takempf]

Due to the following:

• grunt-init is being deprecated
• It's cumbersome to manage a second repository for the default site template (and constantly update the version number of solidus it needs to use)
• We may stop using grunt entirely (for the speed benefits in gulp)

I think we should investigate moving the site template into solidus itself (possibly using some other initialization/template library). Then we could create new sites with the global solidus command: solidus init.