First attempt at route arrows

wrong direction, and far too many arrows :/
Try mucking about with the arrow size and direction

but no joy yet
Use quantity instead of weight

as variable/object property name

And fix some tests that became broken
Make tests pass consistently
Merge branch 'master' into routearrows1

* master: (32 commits)
  Make tests pass consistently
  Use quantity instead of weight
  Deduplicate HTML fragments
  Correct label elements in html fragments
  Fix the CSS to work with new classes for location filters
  comment out variables that use d3 maybe before it's loaded
  Generate the country select list properly
  Allow filtering by year range
  category filters selection now changes paths shown on map
  Wire in the select boxes
  disable the country and year dropdowns
  making widths of inputs the same and tidying up file browse fields
  hiding labels and legend
  Dynamically create the category selections
  Dynamically create form/to year form elements
  styling filter panel and general interface
  add callback for filter loading
  Windows doesn't appear to record file.type
  Load form bits from html fragments
  Move divs around slightly
  ...

Conflicts:
	trademapper/js/spiralTree.js
Put white transparent arrows on segment ends

(which are actually segment starts due to the way we draw them).
Have separate wide and narrow arrows

depending whether the path is big and wide or small.  Might still need
some tweaking