core: re-design memory allocator (fix #1091)

* Core_mem_allocator: implement Range_allocator interface
* Core_mem_allocator: allocate with page-granularity only
* Use slab allocators in core where meaningful (e.g. dataspace objects)
Remove outdated sections from doc/architecture.txt

Fixes #71
pandaboard: prevent copy of non-copyable objects

Follow up fix for commit 0b7ea4abab
Ref #1093