Integrate with distinst's new autoinstall features

[mmstick]

• Opens the door to retaining home and supporting refresh installation options. The logic is implemented here in the frontend, but will also need a UI to take advantage of it (listing refresh options & setting retain_home in the config).
• The backend now handles more of what the DiskView was previously doing, so when a disk is selected, the EraseOption for that button will be stored and applied in the ProgressView.
• For each entry into the DiskView, a global Distinst.Disks will be used for generating the list in the view, and Distinst.device_layout_hash() will be used to know when the Disks object needs to be regenerated.
• Removes the default_disk_configuration() method due to the backend now supporting it via applying the EraseOption to the disks object.
• Removes the recovery_disk_configuration() method due to the backend now supporting it via applying the RecoveryOption to the disk object.
• Merges elementary@f2a6aec

Requires pop-os/distinst#95

[mmstick]

@brs17 @jackpot51 This is also ready