[EHPweb] Left Navigation proposal

[Jeremy Fee]

I was looking at the navigation files, Lisa asked me to document them,  
and I think we can further simplify the way navigation is included in  
the template.  The idea basically mimics how breadcrumbs are scattered  
throughout the site with their content.

Let me know what you think,

Steps
	- scatter navigation files as _navigation.inc.php throughout document  
root, the underscore makes it first in a directory listing
	- define a new template variable $LEFT_NAVIGATION
	- if a page does not set $LEFT_NAVIGATION, the nearest file (crawling  
up the tree) named _navigation.inc.php is the default
	- update navigation.master.inc.php to use $LEFT_NAVIGATION variable
And, optionally
	- update layouts to remove navigation.master.inc.php