Allow user to get instrument definition file without specifying
a date, in this case the current date will be used.

refs #3640 save par saves ASCII par file but more tests are needed to be sure that it saves exactly what people expect

Continue obsession with const: ExperimentInfo(MatrixWorkspace)::getInstrument now returns a const instrument. Re #1944.

Refs #3669: Refactored LoadInstrument by moving the parsing code to Geometry/InstrumentDefinitionParser. This allowed ExperimentInfo to use it to load the instrument directly.

Refs #3669: instrument XML contents are saved in NXS processed file. Much more painful then it needed to be.

ExperimentInfo::getBaseInstrument() is gone. If it's really necessary to get hold of the 'naked' instrument then there's a baseInstrument() method on Instrument itself - but it should only be rarely needed. Re #3690.

Refs #3689: Modified saveNexusProcessed to use the methods in the Sample and Run objects. Sample logs split into 'logs' group. Still backwards-compatible with existing NXS processed files.

Add pointer to physical instrument as a member (not used in vast majority of cases) of Instrument. Show this 'physical instrument' in the instrument view, if it exists. Re #1944.
P.S. This again lead to a const change which accounts for most of the changes.

Refs #3590: FindPeaks sets the goniometer and run number in the peaks found. It also knows if the workpsace is in Q lab or Q sample frame. Peaks found are ~ the same from either type of workspace.

Eradicate IInstrument. Instrument's the one to talk to now (it was the only descendent class anyway). Re #2041.

Fixes #3524: PeaksWorkspace inherits from ExperimentInfo so it carries a sample object, instrument, etc.

Refs #3202: Moved out NearestNeighbors from the ParameterMap to the MatrixWorkspace, thereby de-mingling the spectraDetectorMap and the instrument. Made a ExperimentInfo class that holds info about an experiment that will be shared by a few workspaces: Instrument, Sample, and Run.