Added "Free disk space"

[lianergoist]

I like to let the users see how much free space there are available on the disk.

I use the php-function disk_free_space() to get the numbers, and do some number formatting to make it readable.

I also needed to add "FreeSize" to translation.json

<?php 
  $mybytes = disk_free_space($root_path); 
  $mysi_prefix = array( 'B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB' );
  $mybase = 1024;
  $myclass = min((int)log($mybytes , $mybase) , count($mysi_prefix) - 1); 
?>

<?php echo lng('FreeSize').': <span class="badge text-bg-light border-radius-0">'.sprintf('%1.2f' , $mybytes / pow($mybase,$myclass)) . ' ' . $mysi_prefix[$myclass].'</span>' ?>
                    
<?php echo lng('File').': <span class="badge text-bg-light border-radius-0">'.$num_files.'</span>' ?>
<?php echo lng('Folder').': <span class="badge text-bg-light border-radius-0">'.$num_folders.'</span>' ?>
<?php echo lng('FullSize').': <span class="badge text-bg-light border-radius-0">'.fm_get_filesize($all_files_size).'</span>' ?>