Add Pre-installed Code Libraries for php and python

[thousandsofthem]

http://dev.iron.io/worker/reference/environment/

Section "Pre-installed Code Libraries (language-specific)"

We have "Ruby Gems Installed" but no corresponding section for php and python

At least php has some modules installed, like GD, mongo.

Full list can be retrieved from build script

[coopernurse]

From: server_images/simple_worker.sh on master branch

PHP:

php5-curl
php5-mysql
php5-gd
mongo (via pecl)

Python:

python-lxml