Optimize : request hostname to system only once and use ThreadLocal for SimpleDateFormat

+ request hostname only once, when the JSONEventLayout class is initialized
+ use a *ThreadLocal<SimpleDateFormat>* instead of creating a new *SimpleDateFormat* for each call to the *format* static method
+ bonus: organized imports (intellij idea style) + format code

I saw a performance increase of 30% on the *measureJSONEventLayoutLocationInfoPerformance* test method on my system.