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
Should I assume v0 mapfile by only setting contaddr_size? If the caller is Pithos, it is supposed to always set XF_CONTADDR flag in parallel with contaddr_size variable?