So if the Beatles tribute band Imagine played "Tax Man," could that be construed as a political message?Douglas County Democrats were riled by the potential that the conservative advocacy group Americans for Prosperity might use the Concerts in the Park to do a little proselytizing.The Friday evening concerts in Minden Park are popular events put on by the Douglas County Parks & Recreation Department with the help of corporate and other sponsors.The only reason the county is able to continue offering the concerts, which draw hundreds of people to Minden, is due to the sponsors, who contribute the lion's share …