Add a javascript runtime gem, change label on new admin view to match login form

The command **bundle rake install** in a clean environment fails after bundling due to missing javascript runtime, which is usually included in the Gemfile by default in a new Rails 4 project. Added **therubyracer** gem to Gemfile, along with standard comment with link to additional information.

The new admin screen that comes up initially upon booting the app labels the first field 'Name', but the subsequent login form asks for 'Username'. This was a point of confusion for me. Changed the label on the new admin view to reference the same label translation as the login form.