Not long ago, DCist bemoaned the lack of a snowball stand in D.C. Now we’ve got word that slushy treats with fruity flavors will be served in D.C. starting on Monday. While many DCist readers pointed out that there are many such refreshing summer sweets to be found in the greater Washington area, Rita’s, which also has a branch on Georgia Avenue in Silver Spring, serves genuine Philly-style water ice. And it has a prime…