Presets no longer supported in bulk_update task

Presets can be updated via Atlas:

  cd path/to/atlas
  bundle exec rake preset:fix
Fix merit:archive to work with the latest Merit gem
Make bulk_update compatible with Ruby 1.9
Weighted carrier cost uses cost_per_mj if present

Instead of traversing all the way to the right-most carrier, stop early
if a traversal path encounters a carrier with a cost_per_mj defined.

Closes #707
Merge pull request #708 from quintel/fix-707

Weighted carrier cost uses cost_per_mj if present