Added issue count to the template

I've made a bit more progress with adding the issue count to the sidebar.

In the current implementation, the following text is displayed when the 'learn' template is rendered.

![screen shot 2014-10-21 at 15 57 09](https://cloud.githubusercontent.com/assets/1098110/4741773/bbf6fb16-5a19-11e4-95ab-798183454c95.png)

After requesting the issue count from the GitHub APIs, the above section is either hidden (if there are no open issues), or updated to include issue count:

![screen shot 2014-10-21 at 16 05 50](https://cloud.githubusercontent.com/assets/1098110/4741796/e4cf9f02-5a19-11e4-8b1a-36be035cb5f5.png)

You can see it in action here:

http://colineberhardt.github.io/todomvc/examples/olives/
http://colineberhardt.github.io/todomvc/examples/emberjs/

And the proposed template change here:

https://github.com/ColinEberhardt/todomvc/commit/2f54500759e06287c542123cb7f2ce0b8bfe8541#diff-719bcdeda5b5e8046f18065efe042e27R2269

This change is close to complete, however one small issue I have is that the identifier I use for each framework in the automated tests is the folder name (this allows me to easily look for all sub-folders in order to build the full test suite). However, learn.json uses the `data-framework` attribute, hence the code here:

https://github.com/ColinEberhardt/todomvc-common/compare/tastejs:master...master#diff-5656e7f7dd4df43f42db8d894c5396c0R195

(which doesn't have any error checking).

A couple of quick questions:

1) Is everyone happy with the cosmetics, i.e. the way that issues are presented?
2) Is the `data-framework` attribute the canonical framework name? If so, I will update the issue labels and change the browser tests to use this name.






If the API is down/weird for any reason, can we check `e.target.responseText` is an array before trying to parse?