Update WorkspaceFactory to use the MemoryManager

[NickDraper]

Currently the Workspace Manager uses the requested size of a workspace to decide wether to create a ManagedWorkspace or not. This is done by comparing HistogramCount*TimeBins to a value in the .properties file.

This should be updated to use the information that can be provided by the MemoryManager. I suggest that we change it so it reads a value from the .properties file that gives a percentage of the available memory that may be used for the workspace. Therefore if they have the value set to 50% then if a full workspace would take less than 50% of the available memory then that would be returned, otherwise a managed workspace would be used.

You will need to do a bit of benchmarking to investigate what a sensible default value should be.

[NickDraper]

This issue was originally trac ticket 206