Added new innerElBorderOffset property to base graph class.

This allows us to adjust the position of the graph based on the border width at the bottom.

Removed some crazy code.

Removed some dead code.

Updated tests.
Use simple lines for line graphs

Line graphs were using stacks with a white background, instead of just being lines.

Using lines instead of stacks keeps the code simpler, since it doesn't add extra "invisible" elements.
Added test for innerElBorderOffset property.
Merge pull request #703 from alphagov/bugfix/graph-stack-fills

Use simple lines for line graphs
Merge pull request #704 from alphagov/bugfix/bottom-margin-on-line-graphs

Added new innerElBorderOffset property to base graph class.
Add config for browser module on DVSA site activity dashboard
Automatically create "other" category for non-defined data groups

Where a group in grouped data does not have an axis/line configured, automatically add its values to an "other" category.