First stab at a new window + user agent sample. User agent override not yet integrated.
- Add global for user agent inject on new browser windows
- Add config parameters for user agents
- Add ContextMenu functions for tracking and manipulating user agent strings
  of new tabs
- Refactor: export createPopup() from popup module to allow tabs module to
  create a popup without an interstitial confirmation (only when user used
  context menu to request popup)
- Bug fix that should also be pushed to new-window sample: use contentload
  event for most things, and only update controls with loadstop event
- Bug fix that should also be pushed to new-window sample: check format of
  incoming messages at guest to bind <title> correctly
- Create new popups and tabs using postMessage() to guest
- Specify supported browsers in config
Remove superfluous console.log and rename title.js to more appropriate guest_messaging.js
Adding new-window-user-agent sample assets and readme
Touch up readme links
Touch up readme to refer to GoogleChrome/master in preparation for pull request
Merge pull request #250 from mdittmer/new-window-user-agent

New window user agent sample webview-samples/new-window-user-agent