Update of the Getting Started guide

The getting started page has been compartimentalized in 4 different things to install (Java, GitHub, Maven and IDE), and each one is chopped in 4 different sections (what it is, why you need it, do you have it installed, and installation) for easier skimming. A couple of 'do you have it installed' are obvious, as well as the explanation about what Java is, but it helps keep a matrix structure and makes is more readable.

Also, a new 'dependencies' file has been created with POM stuff that was not necessary to get started. I would consider merging this file with the 'downloads' or some other but I would need to understand the global picture first.

Notes: The video is a little bit outdated now, but it is still understandable