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.
scratch that,

 https://getcomposer.org/doc/articles/vendor-binaries.md#what-happens-when-composer-is-run-on-a-composer-json-that-defines-vendor-binaries- 

I misread that, that would not work for cakephp/app

Still, i think we should keep vendor/bin as default directory for vendor binaries per earlier mentioned reason. Users can easily create a symlink themselves if they want a single place for all binaries