[basic.memobj] Provide a logic progression of subclauses

Reorder the subclause of [basic.memobj], Memory and objects, into
a logical progression where each clause augments the one before.

Memory model specifies the notion of memory for C++
Object model specifies objects, and how they occupy memory
Alignment restricts where objects can reside in memory
Storage duration describes how objects acquire well-aligned memory
Intermediate and erroneous values specifies the initial contents of acquired memory
Lifetime describes the validity of objects within their acquired storage
Temporary objects have a lifetime of their own.