store ProductProperty instances in PHPCR

credits: https://github.com/lsmith77 and https://github.com/stewe

This is a proof of concept to store ProductProperty instances in PHPCR, rather than using the standard EAV approach.

This has several advantages:
1) no longer limited to VARCHAR(255), meaning that now longer strings, dates even binaries are supported
2) multi value properties are also supported
3) its possible to query these fields without joins

The disadvantages:
1) overhead of the listener
2) its no longer possible to queries the properties along with the other product fields via an SQL statement