refactor code in a private method
File Download Report
 + add user data model - the return value of new metric
add UserDataReader to read a user's data from a record
add filter for file download report metric
add a new DAO interface to support file download report metric
rename some classes and add an implementation for FileDownloadInvDao
add namespace for file download metric
complete the implementation of put method
complete the getTop() method in FileDownloadInvDaoImpl
update UserDataPoint and UserDataReader
add FileDownloadReportMetric
use Key.SEPARATOR instead of ":"
refactor code in UserDataReader
add new service in ReportWriter to handle reportMetrics
Implement Metric Writer for the new Metric
create a util class to get the entityId from a download Uri
set Key class' visibility back to package scope
rename DaoImpl file
remove UriUtil class
clean up some comments
complete get() method in FileDownloadDaoImpl
remove UriFileDownloadFilter class
add method to get the EnityId from a download Uri
add getFileDownloadReport method in metric reader