Load d3.js locally

I replaced the remote version from d3js.org with a local version
copied from the dc.js example page.
Remove style related to ul element, formerly used in a form
Rename show/hideSvgCode() to show/hideCodeBlock()

The specific names predate the move of this code for more general
use in the interactivity-utils module.
Display the total number of categories next to each filter
Hide select list borders except on hover
Add space before '/' followed with total values of a list
Rename CSS classes used for layout, now using -area suffix

I renamed 'visualization' to 'main-display-area'; I will
reintroduce 'visualization' within, distinct from a new
element for the filtered list of authors and categories.
Extract new utility function showBlock() and hideBlock()
Add list to display either the visualization or the data

I added a JavaScript module for the selection behavior,
and markup in the HTML document with a select list and
one option for each block.

There is nothing specific in this function, which could
be moved to interactivy-utils module if it needs to be
reused.
Add warning with explanation of expected markup for display selection
Apply the initial selection (selected value remains on refresh)

I had to move the script definition after the definition of each block,
which were otherwise undefined during the initial invocation.
Define name attribute on select element, not option elements
Merge branch 'enhancements'