Rename HCIPostProcAlgo and HCIDataset

[r4lv]

Being the new preferred entry points to the world of VIP, I think the HCIDataset, HCIFrame and HCIPostProcAlgo classes could be renamed to something shorter: that would be easier to type and easier to remember. I propose:

• HCIDataset → Dataset ("HCI" seems redundant here, as HCI is the purpose of entire VIP)
• HCIFrame → Frame
• HCIPostProcAlgo → Postproc

and maybe

• HCIPca → PostprocPCA etc.