[reSIProcate] Header Template class

[david Butcher]

SipMessageExplicit is not used. We switched from templates to macros quite
awhile ago. In effect, SipMessage is explicit.

There are #if'ed out references to templates just to add to the general
confusion.  An early design did template tricks that were deemed likely to have
platform issues.

We should probably relegate the header template stuff to archive...

Quoting Thomas Gal <ThomasGal at LumenVox.com>:

> Can Anyone tell me where the Header Template class is defined that is used
> in SipMessageExplicit?
> 
> -Tom
> 
> thomasgal at lumenvox.com  
>