Generalize FileListAdapter parts

At the moment The FileListListAdapter and the LocalFileListAdapter offer to render the file listing as a list or grid (with a special threatment of images/videos). Right now the code to pick and configure the list and grid item are code duplicates.

This issue is for discussion and solution finding. The "problem" here is that at the moment the local adapter works with a collection of File, while the FileListList adapter works with a collection of OCFile, so some calls differ, most do not.