Hook in BarSeries

Introduces the BarSeries as a new common base class between Row and
Columns, and plugs it in.

Currently, this does not hold any functionality of its own.
Separate row/cols in css classes

Both RowSeries and ColumnSeries were using the same classValues. Here,
we create a new one for each Row and Column, keeping BarClass for
BarSeries.
Pull common functionality up

Almost all of the code is shared, so could be pulled up.

For now, there are some slightly messy instances where some methods are
different for cols and rows. I'll be cleaning these up in future commits
Remove duplication from key positioning

The only difference between rowKeyPosition and colKeyPosition was
whether they used barBreadth or barWidth, which is already decided by
the "width" value.
Moved insight.Scales into its own file
Fix BarSeries highlighting

The changes in class naming had broken highlighting on selection. Here,
we make sure the classes are reapplied to all bars, not just the ones
being clicked.
Remove duplicate barLength function

We had a barLength and a colBarLength method. This way, we can
consolidate them together.
Merge branch 'upstream' into feature/bar-series
Update Changelog
Added documentation for scales
Using lowercase for insight.scales
Updated change log
Responding to review comments
More review responses

Missed this one out!
Update initial tick to ensure it is a multiple of the tick frequency

Add tests to describe the expected behaviour.
Fix initial tick to use UTC dates for a date axis
Update changelog
Document series data types

Series can be an insight DataSet/Grouping, or an Array of
numbers/strings/objects.
Moved Scale class to insight.scales namespace
Merge pull request #234 from tpkelly/feature/bar-series

BarSeries