Cleanup mojo_shell and sample_app a bit

Cleanup mojo_shell and sample_app a bit

This CL contains a number of cleanups now that the structure of mojo_shell is
clearer. Specifically,

1) I've moved sample_app.cc from mojo/shell to mojo/examples/sample_app. The
   sample_app isn't part of the mojo_shell. It's an example app that runs on
   top of the shell.

2) I've merged mojo/loader into mojo/shell. Originally, I thought it would be
   better to keep the loader separate, but we had to introduce a direct
   dependency from mojo/shell to net anyway, so we might as well merge these
   two directories. We'll probably pull them apart again when we can make the
   loader into a Mojo service.

   As part of this cleanup, I've also removed the Job/JobImpl split because
   that existed only to avoid leaking net headers. This ended up simplifying
   the code a bit.

3) I've renamed mojo/shell/android/shell_apk to mojo/shell/android/apk to
   remove some of the stutter from the directory name.

4) Finally, I've added a Quit task to run.cc in the error case so that we exit
   the main loop when we hit this error instead of spinning forever. This
   change is the only behavior change in this CL.

R=darin@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=231287

[darin (slow to review), 2013-10-27 22:43:49]

LGTM

[commit-bot: I haz the power, 2013-10-28 00:14:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/47433002/1

[commit-bot: I haz the power, 2013-10-28 06:28:40]

Change committed as 231287