[iso] update libcdio to v0.93

* Also fix a memory leak introduced vy v0.93 in cdio_free()
[misc] fix the display of "task x/y" when formatting

* Using the famous URS™ (Under Rug Swept) technology
* Closes #182
[ui] fix unwanted behaviour when ISO is unsupported

* Remove "Scanning Image..." from status, and prevent the Start from being enabled when no drive is selected
* Closes #375