Make creating an instance on Heroku smoother

[sethherr]

• Mention the fact that it requires a verified account on Heroku
• Update bundler (or rubygems?) in Gemfile.lock so it doesn't give warning on Heroku
• Reformat the "replace sh-example-app" text and capitalize sh-example-app to make it clearer that it needs to be replaced
• Add an ID column to the priority example to provide an example with IDs (so no need to remap)
• Remove the empty column in sh-example-priority app on Heroku