Consolidating feed functions

Reorganization of some functions into a single feeds file
Rename discover-feeds.js to query-google-feeds.js

Name the file to match its function to be a bit more consistent with
other file naming conventions in use
Deprecate map and set shims

Chrome stable appears to be around 39 at the moment on all platforms.
Set/Map appear to be stable across all platforms. Therefore there is no
longer a need for these shims.