add support to Rename, change background color, bugfixed

• support to Rename current image file, only for folders
  • requested by @Gitoffthelawn issue #7
• support to change background color, can be checkered pattern
  • requested by @anantoghosh issue #10
• bugfixed: if set max volume cache < 4, changing the volume resulted in an unauthorized termination
• bugfixed: If the volume is already read, even if you specify the file of the folder and open the volume, the read file was opened