EventList: implement weights for individual neutrons to allow division etc. on EventWorkspaces

[Janik Zikovsky]

It is desired to be able to keep an EventWorkspace further in the process, including after dividing spectra, for example.

• The EventList will hold either a list of TofEvent (without weights) or a list with the weights (a new structure with weight and error fields).
• Hide the details from EventWorkspace as much as possible by making EventList handle the conversion as needed.
• Rebinning code will need to handle the summing of weights and errors etc. properly.
• Possibility: subtract two event list = EventList1 + (EventList2 * -1) ? This means having _negative_ weights on some events, but why not?

[Janik Zikovsky]

(In [7016]) Refs #1763: first check-in of weighted event lists, and lots of tests for them.

[Janik Zikovsky]

(In [7017]) Refs #1763: Added divide methods to EventList.

[Janik Zikovsky]

(In [7019]) Refs #1763: Fix for NAN in windoze, and more doxygen.

[Janik Zikovsky]

(In [7020]) Refs #1763: Test portable isnan.

[Janik Zikovsky]

(In [7024]) Refs #1763: Fix test.

[Janik Zikovsky]

(In [7711]) Refs #1763: Fixed the error propagation formula for dividing weighted neutrons.

[Janik Zikovsky]

(In [7712]) Refs #1763: added an extra test for histogramming weighted events.

[Janik Zikovsky]

(In [7713]) Refs #1763: Fix windows test build; more doxygen formulae.

[Andrei Savici]

Works

[Stuart Campbell]

This ticket has been transferred to github issue ​2610