filechooser for destination folder selection and other minor changes.

[dentex]

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!