Remove croutonticks, as it is no longer necessary.

https://gerrit.chromium.org/gerrit/#/c/45317/ has trickled down to stable.
Check if make_dev_usb has run; if so, enabling vboot bricks the system.
Fix croutoncycle on some systems.
Make gnome-session-wrapper executable in the repo.
Get rid of crusty old intentionally confusing README language.
Special-case the internal trackpad in croutonwheel.

Fixes #149, although additional work is needed to support external trackpads.