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/models/airtime/map/CcMusicDirsTableMap.php

@@ -41,6 +41,7 @@ class CcMusicDirsTableMap extends TableMap {
 		$this->addPrimaryKey('ID', 'Id', 'INTEGER', true, null, null);
 		$this->addColumn('DIRECTORY', 'Directory', 'LONGVARCHAR', false, null, null);
 		$this->addColumn('TYPE', 'Type', 'VARCHAR', false, 255, null);
+		$this->addColumn('EXISTS', 'Exists', 'BOOLEAN', false, null, true);
 		$this->addColumn('REMOVED', 'Removed', 'BOOLEAN', false, null, false);
 		// validators
 	} // initialize()