Add an option to LoadRaw to skip the loading of log files

[mantid-builder]

Original Reporter: Russell Taylor

The diffraction people don't care about log files when they're doing their day-to-day data analysis, yet when they're loading from one of the large archive directories they have to wait for 25s or more while it searches for log files to load.

If we can't find a way to dramatically speed up this directory searching, then we should add the option to LoadRaw to skip LoadLog (the default should still be to load the logs though).

[mantid-builder]

This issue was originally trac ticket 848