CC-2977: Never delete files from the database

- Files are marked deleted(file_exists to false) on deletion.
- Dirs are marked removed(removed flag to true) on removal of watched
folder in a usual way. If dir is unmounted, without being removed from
watched list first, it will be marked as not exists(exist flag to false)
- Manage Media Folders will show if dirs exist or not( mounted or not)
- Playlist builder will show if files exists or not

airtime_mvc/application/views/scripts/playlist/update.phtml

@@ -17,6 +17,7 @@ if (count($items)) : ?>
             </div>
             <div class="text-row">
                 <span class="spl_artist"><?php echo $item["CcFiles"]['artist_name'] ?></span>
+                <span class="spl_artist"><?php echo ($item["CcFiles"]['file_exist'])?"":"NO FILE FOUND!" ?></span>
                 <span class="spl_offset"><?php echo $item["offset"]?></span>
             </div>
             <?php //create the crossfade icon.