Renamed more explicit to avoid overlaps

Renamed `update_selections` to the more explicit `update_user_selections` to avoid function name overlaps when developers derive their applications from the `gae-init` family.

I learned the hard way that a copy-paste-find-replace `user.coffee` to `whatever.coffee` didn't brew in production... while it did on development. The `whatever`s didn't select properly... as in fact, the code was trying to make `user`s of `whatever` by over-re-using the `user`.`update_selections` :-)