Use a single Fragment for all planets

I liked the look of this app so wanted to try and make some improvements to the way new Fragments are added to the pager. I've only spent around half a day on it so I haven't completely optimized everything but the general concept and idea is there. My general intention was to reduce the amount of code written and make it re-usable. Using this as a base it is relatively simple and quick to add new planets or moons and to also change the styling or layout of the planets pages because it now only has to be done in one place. 

There was a fair amount of code duplication in the original which I've been able to reduce.

Good work, keep it up. If I can help any more let me know.