The final goal is to use the same process for the search provider and
the application, to make it easy to support the new shell search
provider API. In order to do this, some things that are currently global
in Documents cannot be assumed global anymore - for example, the currrent
search string cannot be shared between the provider and an existing
window; we basically need to keep the search provider state separate
from the rest of the application.

This commit:
- moves all the code related to search attributes in search.js
- removes global.js and moves the state and controllers to Application
- adds support for a different "context" to Manager and the shared
  controllers
- moves ShellSearchProvider to be created from the application, with a
  --no-default-window option, and separate states/controllers
- modifies Application, Embed and others to handle the provider service
  and closing/reopening of a window