Check availability and install missing modules

the webclient install process checks for the needed modules and versions and installs missing ones

IMHO this should be the case for all OpenERP modules (server, gtk, koo)

a script load_modules.py would at least check if all modules are available - so far it contains
import psycopg2
import reportlab
import pychart
import pydot
import mx
import xml
import lxml
import libxslt
import pytz
import vobject