filechooser for destination folder selection and other minor changes.

Hi, I added something:

    filechooser for destination folder selection;
    lots of imports removed (by eclipse...);
    vertical and landscape layouts redesigned (mostly rearranged);
    some hardcoded paths changed with android.os.Environment paths;
    block SlidingMenu if exiting from the folder-chooser.

I downloaded the `.apk` from the repository but the app freezed the phone.
Then I realized that the ffmpeg binary was not stopped, so probably I ended having multiple jobs running at the same time.
All started because of this. I wanted to see what was wrong, but the version directly compiled in Eclipse worked. 
Then I started making the changes listed above.

CIAO!