Use Foundation Equalizer for Sidebars

The current implementation of full height sidebars has some issues on
really high resolution display settings where the sidebar has no
padding. This changes all sidebars throughout the application to use
Foundation Equalizer instead of using a background linear gradient.
Use asset_path helper in select2 styles with urls.

This also moves the images for select2 into vendor/assets/images and configured
the app to precompile assets in vendor/assets/images.
Merge pull request #371 from opscode/equalize-sidebar

Use Foundation Equalizer for Sidebars
Merge pull request #372 from opscode/select2_images

Use asset_path helper in select2 styles with urls.
Remove html from plain text collaborator email.
Merge pull request #373 from opscode/plain_text_collab_mailer

Remove html from plain text collaborator email.
adding a /metrics endpoint