Addition of Polyglot.js for multi-lang support

This includes a Handlebars helper function 't' which is a wrapper to
Polyglot.t().  More work needs to be done regarding support for
placeholders.
Adding placeholder support for localisation
- Handlebars lib v1.3 added
- Handlebars dev dependency updated
Translation replacements
Implementation of multi-lang support

- Tweaked'lang' routes to allow any languages
- Defaults to 'en' if no language JSON can be found
Merge branch 'Multi-lang_support' of github.com:adaptlearning/adapt_authoring into Multi-lang_support
Removed call to localstorage.setItem()
Removed call to fs.existsSync

Switched this to call fs.exists and reworked app.js to wait for the
language strings to load the first time.
Removed t2() handlebars helper

This is not required.
Merge pull request #306 from adaptlearning/Multi-lang_support

Multi lang support