add getRelated operation to LiveDevProtocol.

Retrieves URLs from documents.scripts.src and document.stylesheets.href
This is an initial iteration that could eventually evolve in CDT-like
protocol to retrieve/track related docs from the browser-side.
Merge pull request #3 from sebaslv/related-docs

add getRelated operation to LiveDevProtocol.
Supporting CSS, part 1
add documentation and minor clean-up
Merge pull request #4 from sebaslv/related-docs

Get related documents from the browser page
initial monitoring of added/removed related docs

based on MutationEvents.
initial migration to MutationObserver interface
fixed the case when live editing starts with a css file.
remove getRelated call from initial sequence

it now entirely relies on events coming from the browser.
all messages are enqueue and sent once transport is connected.
fixed some issues:
- isRelated implementation
- delete related stylesheets
Fixed a few things and added support for nested @import style sheets.
merged from remote.
merged from sebaslv/related-docs
fixed current doc url in _open
fixed jslint issues
add DocumentObserver as watcher for related docs

- code re-organization
- fix initial sequence (initial event with all related docs + watching)
- remove msg queue (related docs observation starts now after document
  is already loaded)
- adds handler for related docs in LiveHTMLDocument
change method name from getRelated to Related

There was an inconsistency in previous commit btw
DocumentObserver and protocol.
Merge pull request #5 from sebaslv/related-docs

initial monitoring of added/removed related docs
merged from sebaslv:shahabl-feature/css
removing jslint issues.
fix JSLint issues

switching from JSHint