refine the use of scope in custom library api

[yourhead]

ExtraLib has always had a scope property. This is a refinement to define control the injection point by using the scope:

• scope: site (default unchanged behavior) head link to rw_common published file. nothing in edit mode.
• scope: page (new behavior, opt-in) content injected in the page-js or page-css file. css included in edit mode.

this provides a way of sharing the most commonly shared content from multiple stacks (css, js) without the need to add multiple head links or multiple copies as templates.

all library content is static. no templates.

[yourhead]

NB: injection to edit mode happens for each stack. this is to maintain a standalone dom element that contains both style and content for each node. this reduces the efficiency of using including css in many stacks, however there is little alternative. DOM isolation of nodes is likely to remain a hard limitation until webkit provides cocoa mechanism to utilize a shadow-DOM (and we all know that is never going to happen)

[yourhead]

in beta 17