referencing current card and parts in inclusions+solution

_self / _whole = the card the inclusion is on (this is implemented - we need to validate for no infinite recursions if view:content or view:open)
_left = the left part of the card the inclusions is on (what happens if it's a solo card?)
_right = the right part of the card the inclusions is on (ditto)

base: is now deprecated.

If _left or _right occur on simple cards, each of those is treated like _self