Move cake executables into bin directory

Refs https://github.com/cakephp/cakephp/issues/4347

Note: wasn't sure if we should just leave `Installer.php` in `src/Console`... heh, but I did.  Open to suggestions on a better location or directory name for it.
I would like to see the `bin-dir` config change in composer.json reverted

bin/cake is an application binary, i would not want to end up all vendors binaries in there as well