Fixing account login / adding options for viewing stars

I looked into the issue with logging in and pulling balance and star information (a2#1) and I noticed the response text from the original POST to the sign-in page was showing this:

```
Sign In Unsuccessful
Please enter your Starbucks username.
Please enter your password.
```

So, it seemed that it wasn't getting the POST data at all.
After adding in the content-type and content-length (for good measure) to the initial POST request, it began to successfully login and retrieve data as expected. Previously I was never once able to log in.

After finally getting the login to work, I noticed that my stars were at 0. I found in the code that it is pulling the "amount of stars remaining until the next free drink". Since I'm currently a Green Rewards member, this will always be 0. It would be much more useful to me if I could see my current number of stars, though I know for others the original number is better.

I added in an option on the gh-pages branch (see second pull request) for choosing which star type you want to see (along with the back-end code for populating the dropdown and returning the value). I then added the necessary code to the pebble-js-app.js file in this master branch to pull the preference from the storage area and pull the appropriate star number from Starbucks.