No selecting stack in no data section
Wrap entire realtime module in a paragraph tag

And then use spans to style the impact number.

This involves making the CSS matchers for impact-number and stat-description
more loose, but I don't think that's a problem.
Refactor header Sass into header.scss
Move tagline outside of h1

Keeping it in the header element, but moving it outside of the h1
is better for accessibility.
Fold 'copy' into 'tagline'

It doesn't seem worth it to have two separate fields in Stagecraft
(copy and tagline) that are both styled almost identically.

Add a new 'with-related-pages' class to control the width of the tagline.
Add rightHandGracePixels to hover.js

These few pixels increase the size of the hover area for the middle
section of a graph with linelabels to the right.

Before: as soon as you move from the final date value of the graph
into the linelabel, the hover disappears.

Now: the first few leftmost columns of pixels of the linelabel are
assumed to be hovering on the graph still.
Use NTA Tabular Numbers everywhere

No really, everywhere.
Add WAI-ARIA attributes to graph elements

This commit adds role=presentation and aria-hidden=true to all
SVG elements and figcaptions used for linelabels.

This prevents screenreaders from reading out the elements.

As noted in the comment, the WAI-ARIA spec says we may do this
with caution to improve the experience for assistive technologies.
Minimum viable GOV.UK dashboard

- Add new stagecraft stub for a GOV.UK dashboard
- Allow the tagline to accept HTML so it can contain links to external
  pages
Add realtime usage module to GOV.UK dashboard
remove comments, add explanations of hacks, use constant for LABELS_OFF
better getValue for tooltip with explanation and working tests
Revert "Merge branch 'master' into stacked_graph_improvements"

This reverts commit 79c1d8205b0993eb401205dfb82bd65cd45403d4, reversing
changes made to f87c0597f8cbd2b2e6ab2f7b467dbe675c7d71ff.