Customer loyalty has to be earned, and marketers can win this devotion by meeting shoppers' expectations across channels, says new data from AppDynamics, showing that performance of retail websites and mobile apps can significantly impact customer satisfaction, loyalty, and spend. 70% of respondents say that the performance of a mobile app influences their perception of the retailer.  Sometimes these perception impacts are positive, says the report. A third of respondents say they use apps for convenience, like when they're visiting a store or looking to make a swift, on-the-go purchase. Likewise, 40% say they'd try a new app if …