remove and removeRecursively should be run in background threads

- (void)removeRecursively:(CDVInvokedUrlCommand*)command
{
    // arguments
    CDVFilesystemURL* localURI = [self fileSystemURLforArg:command.arguments[0]];

    [self.commandDelegate runInBackground:^ {
        CDVPluginResult* result = nil;
        if ([localURI.fullPath isEqualToString:@""]) {
            // error if try to remove top level (documents or tmp) dir
            result = [CDVPluginResult resultWithStatus:CDVCommandStatus_IO_EXCEPTION messageAsInt:NO_MODIFICATION_ALLOWED_ERR];
        } else {
            NSObject<CDVFileSystem> *fs = [self filesystemForURL:localURI];
            result = [fs recursiveRemoveFileAtURL:localURI];
        }
        [self.commandDelegate sendPluginResult:result callbackId:command.callbackId];
    }];
}