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.
Another way to keep all binaries in a single place, is to move back `cake` from cakephp/app/bin/cake to cakephp/cakephp/bin/cake and define the `bin` config there.