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.
One problem with moving the bin stub is that it won't actually do anything in the cakephp/cakephp repo. Is it a good idea to have a non-functioning script in the repo?