Liferay Mobile SDK Chapter

Here's the first draft of the Liferay Mobile SDK chapter. I incorporated Bruno's feedback into the Intro and Android sections, and based the iOS format off of the Android section. 

I created the Mobile SDK chapter as Chapter 8 and renamed all of the preceding chapters accordingly. As you know, chapter 7 is the LDS workflow section that is currently hidden.

Thanks!

https://issues.liferay.com/browse/LRDOCS-849
@brunofarache