Increase fluency when scroll/select page.

see: ViewPager.java -> setOffscreenPageLimit(int limit)
    If you have a small number of pages (3-4)
    that you can keep active all at once, less time will be spent in layout for
    newly created view subtrees as the user pages back and forth.
Add support for app to operate in Landscape mode.
Merge pull request #16 from karora/master

Add support for landscape orientation
Merge branch 'master' of https://github.com/MiCode/FileExplorer into jellybean