Incremental commit

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Add stdext/extentlistSet as "extents"

We will use this module to track allocations (as opposed to mappings)

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Use new extents allocator, remove LVM dependency

Signed-off-by: David Scott <dave.scott@eu.citrix.com>