Added Objectify support

Added Objectify dependency to POM and annotated all model IDs and
Entities
Improved PlaceholderFeedItem Report template
Fixed PlaceHolderFeedReport Unit Test
Adding in summations for AdExtensions reports, Part 1
Merge branch 'master' of https://github.com/googleads/aw-reporting into dev
Fixes for AppEngine and BigDecimals
Merge branch 'master' of https://github.com/googleads/aw-reporting
small fix
Fixes for Objectify
Adding in summations for AdExtensions reports, Part 2
Adding in summations for AdExtensions reports, Part 2
Merge branch 'master' of https://github.com/googleads/aw-reporting
Changes to allow report file writing to File System or Google Drive
merging from master