Create a WorkspaceRawFile workspace type and alter LoadRaw to use it.

[NickDraper]

At the moment the first workspace created from a LoadRaw is an exact memory copy of the data in the file. The idea here is to save memory by only creating a workspace type facade that loads the data from the file as it is required.

Things to consider
- Instrument and spectra-detector table etc – this associated information should be loaded in full as normal
- Loading data on demand – It will probably be necessary to load the data in ‘chunks’ of n spectra
- What if an algorithm tries to modify this workspace? – This workspacetype should be read only. If someone tries to modify it it should copy all of it’s data into a normal Workspace2D (or ManagedWorkspace2D) to continue.

[NickDraper]

This issue was originally trac ticket 190