fix(test) - use a real uid/code when verifying emails in complete_sign_up.js test

fixes #561
lint all the files!
feat(build): Add a `grunt version` task to stamp a new version.

* Adds grunt-version and grunt-conventional-changelog dependencies.
* Updates the version number in package.json
* Updates CHANGELOG.md
* Creates a tag.
* Commits everything.

Closes #496
feat: Add a styled 404 page, rendered on the back end.

* Add consolidate middleware to handle the interface between express and handlebars
* Add a middleware to respond to 404s
* Add a branch to the 't' handlebars helper to deal with 't' when invoked in templates written using res.render
* Update grunt tasks to manage dist mode server rendered templates.

BREAKING CHANGE:
The production configuration script must add a new option to its config :
```
   page_template_subdirectory: 'dist'
```

issue #554

.
fix(style): Fiding duplicated selector in main.scss
refactor(i18n): use dependency injection to pass i18n instance around
Merge pull request #589 from mozilla/issue-554-four-oh-four-style

feat: Add a styled 404 page, rendered and translated on the back end.
Merge pull request #592 from pdehaan/po-lint

feat(polint): Lint the i18n .po files
Merge pull request #595 from mozilla/issue-561-real-uid

fix(test) - use a real uid/code when verifying emails in complete_sign_up.js test
Merge pull request #604 from pdehaan/issue-599

fix(style): Fixing duplicated selector in main.scss
refactor(config): change default language to en-US rather than en
fix(styles): Removing unneeded vendor prefixes
Merge pull request #594 from mozilla/issue-496-changelog

feat(build): Add a `grunt version` task to stamp a new version.
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