Refs #11209

Currently nothing will compile.
Refs #11209

Refs #6428 Removed unnecessary read only check. Could prevent issues where a file is changed from read only to not writable.

Refs #6428 Added method to DiskBuffer to set free space blocks (for loading). In getDiskBufferFileData() the free space blocks information is now set after reading the free_space_blocks group from the NeXus file.

Added return option, which tells if the data group already exists

It is pain to have BC shared pointer in Nexus loader. It is also question if it needs access to box controller at all. This is why it is currently accessed through const pointer

It may be not very efficient file mode as one needs to identify the if the buffer for SaveMD make file based is defined correctly.

fixed minor error related to this.

modes