Can install Bolt with composer

Changed some dirs to a define. Define is set to current (default) value unless previously set to something else, or if the path matches the path as installed by composer (vendor/bobdenotter/bolt) it uses that.
Added a scripthandler to install the public webroot files to a public dir (needs the filesystem component).
More info here: http://www.zobriuz.com/blog/installing-bolt-with-composer