Improve hard disk and DVD image handling

[StrikerX3]

The current image loaders are very basic. They rely on the C file management functions (fopen, fread, ftell, etc.), have no caching mechanism, don't implement write-on-copy as advertised, have poor performance, and so on. They also only support raw hard disk images and game discs in the XISO format.

The current implementations live in core/strikebox/hw/ata/drvs/drv_vhd_image.(cpp|h) and core/strikebox/hw/ata/drvs/drv_vdvd_image.(cpp|h).

For this issue, the goal is to:

• Create an abstraction for image loaders in order to support different formats, such as QEMU's QCOW2 format and other popular formats, perhaps even a custom format that embeds media information if that turns out to be necessary, and virtual disks/DVDs that directly access host folders;
• Improve performance by using platform-specific features such as memory mapped files; and
• Pave the way for new features such as the ability to read audio CDs or video DVDs in the emulator.

It may be necessary to implement new ATA/ATAPI/SCSI commands to support these features. Refer to the following specifications and manuals:

• AT Attachment with Packet Interface Extension (ATA/ATAPI-4)
• SCSI Architecture Model - 3 (SAM-3)
• SCSI Primary Commands - 3 (SPC-3)
• SCSI Block Commands - 3 (SBC-3)
• SCSI Multimedia Commands - 3 (MMC-3)