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
Here from the value of args which can be: archipelago:volname:mport=1001:vport=500:assume_v0:v0_size=1245

we only want to keep the second value, the volume name, which must always be there, and always after 'archipelago' tapdisk' type