Add placeholder buttons

Adds some "Show me the code" buttons, to attach the logic to.
Currently, these do nothing.
Import tooltip library

Imports a basic tooltip library, which allows for ajax requests for
tooltips. We can use this to request the source code directly from the
page, or return some pre-formatted code.
Separate index charts into files

Takes the genre chart, language chart and bubble chart, and places the
source for each in its own file. This is to allow the tooltip to request
the source for each individually with an ajax call.
Hook in tooltip

Displays the source code on hover. Currently working on the issue with
line breaks.
Fix newline tooltip issue

Updates the style to use the tooltip content as-is, instead of removing
linespacing.

Also updates the buttons to display on-click instead of mouse over. The
tooltips will disappear when mousing away.
Small code tidy-ups

Removes some of the more verbose parts of the snippet code, as it was
making the tooltip excessively large.

Also changes the </br> tag in the bubble chart on-chart-tooltip for a
"\n", as this was being interpreted by the show-code-tooltip as HTML to
apply, rather than as something to be in text.
Reformats the newline tooltip

Removes the \n or <br> entirely, as this does cause display issue after
all.
Fix $/£ disparity

The tooltip was using $, but the axis and text using £. We now use $
consistently.
Adjust line-height

Makes the text appear closer together, giving a shorter tooltip.
Merge pull request #197 from tpkelly/feature/show-the-code

Show the code
Introduce auto-tick frequency to website
Merge pull request #198 from matthewdunsdon/feature/auto-tick-website

Introduce auto-tick frequency to website
Removed reference to missing closeBtn.gif
Merge pull request #201 from niksoper/gh-pages-dev

Removed reference to missing closeBtn.gif
Merge branch 'upstream' into gh-pages-dev