Replaced simple item list with custom layout.
This new layout means list items will display a 50x50 image on the left
side of the row, and text can take up the rest.
Possible images are: home, cancel, up, image, zip, rar, archive, folder

Increased target SDK to 21 (Android 5.0).

Fixed: very long file names in the list previously went over to a second
line. They will now use ellipsis in the middle.

Fixed: misc notification text in the list.
Notifications (eg. "No recent items") were previously attempting to be
processed, just like files and directories.