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.
`app/bin` is added to git repo but `vendor` is ignored. So this creates inconsistency while the vendor scripts are ignored their executables end up in a dir which isn't.