re-enable sharing statistics

[mmmaaatttttt]

There's a bunch of commented-out code here:

https://github.com/rithmschool/numbers_api/blob/master/app.js#L21-L39

and here:

https://github.com/rithmschool/numbers_api/blob/master/app.js#L48-L91

would be nice to add this back. Right now, there are a couple of problems:

1. The API version has changed, so the commented out code is busted.
2. Would be better to not have code in a setInterval -- instead, let's just get the num shares from within the route handler as needed.

[mmmaaatttttt]

Relatedly, this block seems to be related to the same functionality, this ticket should handle the todo here:

numbers_api/public/js/script.js

Lines 291 to 296 in f864c9b

	// TODO: The leading dot check is a hack to prevent addThis hash tags
	$(window).on('hashchange', updateAllFromHash);
	if (!window.location.hash || window.location.hash[1] === '.') {
	update_history('42');
	}
	setTimeout(updateAllFromHash, 0);

[Nalipp]

Here is the new api.
https://www.addthis.com/academy/developers/
Determine if it is feasible to replicate the original functionality of the share statistics with the new api.

[jacobson-ben]

We should be able to replicate the functionality. However, we need to add a script to the deployed website so that the API can begin tracking shares / visits. The URL and script for this is below:

URL: https://www.addthis.com/dashboard#get-the-code/pub/ra-5e4e232d004d763e

Script: <script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#pubid=ra-5e4e232d004d763e"></script>

Until then, it probably does not make too much sense to write the functionality, as it will be hard to test functionality without website tracking data. Right now, we only get an empty array back from the API.

[mmmaaatttttt]

@jacobson-ben in that case it may make sense to open a separate PR just to include this script tag, and then we go from there. I don't exactly remember the work flow for creating a new deploy but either @Nalipp or I can figure it out. eventually this will hopefully be handled by #12.