Reorganize apps/shell into app, browser and common directories.

This allows us to separate browser process, render process and common code, similar to how content/shell is organized.  This also allows the DEPS files to be more restrictive to enforce those dependencies.

A parallel CL adds apps/shell/renderer and some renderer-specific code: https://codereview.chromium.org/149163002/

BUG=none
TEST=compiles
R=joi@chromium.org, miket@chromium.org
TBR=stevenjb@chromium.org for DEPS on src/chromeos (just moving the DEP from one file to another)

Review URL: https://codereview.chromium.org/151893002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248575 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248575