data-grid widget from Xavier Dutoit @tttp

This commit is 20 commit squashed together; original messages below:

before formatting

new chart data-grid

lazy load images

improve the comments

reindent+default sensible _size

document the expected html function

add the age

age graph on the right

new tests

add the national party

adjust the spec name after you blatantly copy an existing test

calculate avg age

allow to customise the group label

documents the htmlGroup

use CDN for external JS in ep example

thanks @davidjrice for the suggestion!
delint and remove an unused variable

that was causing uglify to complain about side effects
minor documentation fixes
artifacts for PR #500