Add vips and ffi extensions and PHP_EXTENSIONS setting

[baschny]

Added new php extensions:

• vips
• ffi (for use with newer vips PHP package)

Allow to configure an exact list of extensions to load with PHP if you dont want the default (load all). New setting is called PHP_EXTENSIONS. Default is "empty" which is the original behaviour (load all compiled extensions).

All extensions means:

PHP_EXTENSIONS=apcu,bcmath,bz2,calendar,exif,ffi,gd,gettext,imagick,intl,mysqli,opcache,pcntl,pdo_mysql,redis,shmop,soap,sockets,sysvmsg,sysvsem,sysvshm,uuid,vips,xdebug,yaml,zip

A minimal set of extensions that are required for most applications:

PHP_EXTENSIONS=apcu,bcmath,bz2,calendar,exif,gd,gettext,intl,mysqli,opcache,pdo_mysql,yaml,zip

And then add from the remaining one the things you really need:

... imagick,pcntl,redis,shmop,soap,sockets,sysvmsg,sysvsem,sysvshm,uuid,vips,xdebug