Rely completely on CTools content types

CTools has already implemented the pluggability that we want. CTools provides the content_type plugin which have sub implementations like:

• Blocks
• Views
• Panel panes
• Page elements (site name, slogan etc)
• Custom text

I suggest that the ESI module relies completely on the existing CTools plugin content_type. Adding the dependency on CTools is just a win, since it will exist on all D7 sites anyway, now when Views 3 depends on it.

The ESI code base would be rather small and easy to maintain. I'll see if I can make a stab at this one soon.