Add memory chunk reservation API to MemoryManager

MemoryManager allocates paged segments from the provided memory pools of different types (on-/off-heap). Additionally, it can manage reservation and release of arbitrarily sized chunks of memory from the same memory pools respecting their overall limit. The way, how the memory is allocated, used and freed, is then up to the memory user. MemoryManager is just a book-keeping and limit checking component.