Remove NTA Tabular Numbers in header/footer links

Chrome on Windows doesn't link it.

https://code.google.com/p/chromium/issues/detail?id=344347
Merge pull request #314 from alphagov/bugfix-remove-tabular-numbers-from-header-links

Remove NTA Tabular Numbers in header/footer links
Remove "costs" & "other notes" fields from stubs.

These will only be useful when we have Transaction Explorer data
about costs on the dashboards. At the moment, there's no data
about costs being shown - so these are superfluous.

Remove them from Stagecraft stubs.
Update development dependencies

I don't think there's anything in here we need to be too
concerned by.
Remove redundant lint-branch task

There's no lint on master, so if you've introduced lint it is
by definition on your branch.
Update documentation
Merge pull request #313 from alphagov/compile-sass-image-paths-correctly

Compile Sass image paths correctly
Merge pull request #317 from alphagov/update-dependencies

Update development dependencies
Merge pull request #316 from alphagov/bugfix/remove-unused-fields-from-config

Remove "costs" & "other notes" fields from stubs.
Upgrade the frontend toolkit

This includes a change that removes Ruby specific syntax from the
toolkit.

https://github.com/alphagov/govuk_frontend_toolkit/commit/7b0e4ce8b35434238d1df1596f3ef60aff7d526e
Switch from Ruby Sass compilation to Node Sass

It's *much* quicker now. User time:

              Ruby                     Node.js (libsass)
Development   1.199s 0.871s 0.908s     0.486s 0.539s 0.490s
Production    3.627s 3.329s 3.271s     0.581s 0.475s 0.552s
Enable Sass source maps

In development when using a supported browser like Chrome, the inspector
will now show you the Sass file that the CSS originated from rather than
the compiled location.