Show six bars on 'bar chart with number' module.

This is so that we can show six quarters of data by default on the
high-volume bar charts.

Almost all of the high-volume services actually have data going
back six quarters (to Q4 2012) and the more we can show, the
more meaningful the graphs become.

Change font-size on the x-axis labels to 12px: this matches the
font size used for x-axis labels in journey graphs.
Bump Cheapseats version.

We've updated Cheapseats so it doesn't look explicitly for 5 bars
on the bar chart with number module: it just checks that some
bars exist.
Merge pull request #519 from alphagov/feature/show-six-bars-on-bar-chart-with-number

Show bars on 'bar chart with number' module.
Correctly bind function scope in view formatter test
Move threshold for X.Xk format to 10,000
Format 1,000,000 and 1,000,000,000 to 1m and 1b respectively
Remove currency suffix code

It's never used because the only currency we support is GBP
Currency formatter always returns pence for values < 10
Add some extra test coverage for number formatters
Updated test for sigfigs behaviour

Sigfigs only applies to decimals, not to whole numbers. It's a slight bastardisation of the concept of sigfigs, but it works for our purposes.
Handle decimal places for small values in currency formatter.

Values < 10 should have 2 dps by default, and >= 10 should always be integers
Ensure percentage formatter returns unformatted value for non-numbers
Refactor formatters from view prototype to use as uch of standard formatter lib as possible
Remove tests for numbers < 10000 formatting as X.Xk
Completely remove `View#formatDuration`

Use standard formatters instead
Change billion suffix in tests to "bn"
Make zero always return zero
Assorted test fixes
Move numberListFormatter method into main formatters script
Completely remove formatPercentage function

Use standard formatters lib instead