Text changes - Consistency

This patch changes "contact store owner" to "contact us".

In the current (pre-patch) version, messages to store customers, we
sometimes say "contact store owner" and sometimes "contact us"

I believe "contact us" is better and it seems that newer messages in the
current (pre-patch) version say "contact us". It's the older, residual
phrases "contact store owner" that I have changed.