Denver's hot employment market but low single-family home construction activity "is creating a housing shortage crisis that is curtailing affordability and threatening to hold back prospective buyers." That's according to the National Association of Realtors, which Monday released a report saying that Denver is in the top 10 nationally when it comes to "markets in dire need of more single-family housing starts." According to the NAR, Denver needs 67,403 new building permits to get back to a historically…