Minor tidy up for ParComponentFactory pooling

[Martyn Gigg]

The ParComponentFactory was not being used everywhere when creating parametrized objects. Tidy this up and implement the pooling of detector objects.

This should help speed up tight multi-threaded loops that call MatrixWorkspace::getDetector as it caches an object rather than creating a new one each time.

For example,

PARALLEL_FOR1(outputWS)
for(int i = 0; i < nhist; ++i)
{
  IDetector_sptr det = outputWS->getDetector(i)
}

this type of loop does not scale for Parameterized objects as new blocks the threading.

[Martyn Gigg]

(In [9631]) Implemented parametrized detector pooling to speed up loops around MatrixWorkspace::getDetector. The example loop in the ticket for a dataset with ~300000 histograms now takes ~0.3 seconds on an 8-core machine versus 1.5 previously. Re #2528

[Stuart Campbell]

This ticket has been transferred to github issue ​3375