Switched to javascript method of retrieving ReCaptcha images

Fixed several issues that I encountered using this:

* the captchas were too difficult to solve, because it looked to the noscript api. I switched it to the api that the javascript implementation uses, which results in significantly easier captchas (at least, in my experience). This requires one additional HTTP call per public key.
* I kept having conflicts with the inclusion of the apache commons library, so seeing as how the only method used is substringBetween(), I copied that method into this class, and removed the dependency on StringUtils entirely.
* reformatted, renamed, and fixed style issues according to Android Studio's style guidelines