#654 - Standardise and tidy up deviceHandler init return codes.

[emukidid]

I'm using errno where I can but have implemented an extension should devices need to convey something extra about their errors via deviceHandler->status(). I've also tidied up some device handling so this needs a thorough test.

Devices tested so far:

• [x] SD Cards (Slot A / B / SP2)
• [x] Memory Cards (Slot A / B)
• [x] DVD
• [ ] IDE-EXI (Slot A / B)
• [x] Qoob Pro
• [ ] SMB
• [x] System
• [x] USB Gecko
• [ ] FTP
• [ ] FSP
• [x] Wiikey / WASP
• [x] WODE
• [x] GC Loader
• [ ] M.2 Loader