Create a CompressedWorkspace2D and benchmark

[NickDraper]

create a new workspace type that is similar to ManagedWorkspace2D in that is uses a data store and buffers in a most recently used list. However the back end data store will not be a file, it will be a memory block containing the x, y and e vectors compressed using the zlib library (we already link to this somewhere).

Suggested steps:

1. in a test see what the compression rates are for sample workspace data. Investigate the compression/decompression rates.
2. Implement as a new workspace
3. Benchmark the characteristics f this workspace type against Workspace2D and ManagedWorkspace2D
4. Once we understand where it should fit integrate the use of this into the WorkspaceFactory and MemoryManager.

[NickDraper]

This issue was originally trac ticket 765