Add Correlation demo

Uses the app store sample, with interchangeable axes to display
correlation with different data combinations. Displays both the visual
and numerical result.
Merge 'upstream' into gh-pages-dev

Conflicts:
	InsightJS/dist/insight.min.js
	insight.js.zip
Tweaks to correlation

- Moves correlation coefficient to above the chart
- Adds a "selected" class to the last clicked button in the x and y
  categories, and styles it with css.
- References the ErrorContainer class instead of variable name
Reposition "Correlation Coefficient" div

Moved the div above the chart, displaying the correlation coefficient
over the data.
Add wiki link

Adds a link to the pearson coefficient, and rephrases to talk about
variable relationships instead of trends.
Merge pull request #128 from tpkelly/gh-pages-dev

Add Correlation demo