Feature pithoschanges

Includes the necessary changes for better integration with Pithos

Noticeable changes:

* Add signature for v2 maps
* Add v0 map hint
* Support map creation from a given object list
* Remove "archip_" prefix from maps and blocks created by archipelago
* Add rename functionality
* Immediately delete writeable objects when removing a map
* Add readonly option when mapping a volume
This could certainly be done, but wouldn't be better to propagate the UNUSED definition through out the whole code, e.g.  the initialization in XSEG, the initialization on the python code, etc.?

Overall, I think the unused definition, is part of an overall separate protocol, that Archipelago currently does not have well defined. Defining (uint64_t)-1 as UNUSED (or NO_V0SIZE) in the mapper, is just a temporary workaround. 

Having noted the above, I will use the above definition when I resubmit the patch set.