Garden-o-matic: Introduce an option to open links in a new window

- Add a checkbox and have its setting stored in localStorage.
- Update all non-hash anchor targets whenever the settings is changed.
- Honor the setting in ui.createLinkNode (moved from base.createLinkNode,
  since it is a UI-related task, in fact).
- Drive-by: fix (and simplify) tab switching so that disabled tabs will no longer get activated.

R=dglazkov@chromium.org, eseidel
NOTRY=true

Review URL: https://codereview.chromium.org/183923025

git-svn-id: svn://svn.chromium.org/blink/trunk@168439 bbb929c8-8fbe-4397-9dbb-9b2b20218538