Add plugin to handle post_product_id_install
add plugin config file for product_install
Add installing plugins and plugin-confs to Makefile
Add ProductConduit and BasePluginManager

ProductConduit provides a list of installed products on
'post_product_id_install'

Change PluginManager to BasePluginManager, and add a
PluginManager class that knows about the default
config.
make productid call 'post_product_id_install' slot

Also, keep track of a list of the product certs we
install. Pass this to 'post_product_id_install' slot