added php, phpmyadmin + various tweaks to the mix

* ensures all popular php extensions are installed
* adds latest stable phpmyadmin from their git repo
* configures phpmyadmin additional features
* fix vhosts
* increases php memory_limit, post_max_size and upload_max_filesize
* increases apache timeout value
* enables apache mod_rewrite
* ensures git is installed
updated README
added config.vm.box_url in the Vagrantfile