Rewrote toTopoJson.py. Now uses a different folder structure. Handles layers in shapefiles. Removed all the special postcode handling code for now.
Map now displays some planning sectors from Temple Quarter.
Can now multi-select areas on the map. Limited shapefile support to only 1 layer per file.
Multi-select now only happens when you hold the shift key. Put some
borders around the info for multi-selected regions.
Pulled out selection behaviour into separate files.
Completed reorganisation of JavaScript into smaller chunks.
When you select an area, it now displays the details from the joined in
tsv files.
Included missing file d3-extensions.js. Made the details panel now
include both joined in tsv files and the properties which came off the
geometry itself.
Name property is no longer duplicated.
Added a time slider to the map. Numbers in the info panel update over time.
You can now colour a selection according to one of its properties.

This doesn't quite work properly: it doesn't update when time changes
and it doesn't update properly as the group updates.

But it looks nice.
Map colouring now changes with the time slider. Shapes that get added to
or removed from a selection are now coloured or uncoloured respectively.
Removed unnecessary empty source from the starting worksheet.
Added a list of layers which can be clicked to select every item in the layer.
Added a list displaying the sources for the current worksheet.
Colouring now uses the numeric rather than the string values of the data.
Now supports a second tsv file format, with a single column called
constant instead of a time series.
Added support for dragging and dropping in tsv files.
Added csv table import support.
Worksheet is now responsible for notifying various UI components when it
changes.