add information to 'In Memory Files' page

This structure seems exactly the same as "UiFileInfo"  in https://github.com/uronce-cc/tachyon/blob/master/main/src/main/java/tachyon/web/WebInterfaceMemoryServlet.java

How about abstracting it into a class as main/src/main/java/tachyon/web/UiFileInfo.java ? Then two pages can reuse the same class.