Create a facility for neutronic properties of atoms

[Peter Peterson]

The short version of this ticket is to bring in all of the constants from ​NIST into mantid. This will be a new facility in the kernel where there is a bunch of structs that can be accessed through a static method that supplies the symbol (isotopically averaged or select using an alias) or symbol and z-number. This will return a "atom" struct that is read only and consists of the elements:

struct Atom {
  string symbol;
  uint z_number;
  string alias;
  double scattering_length;
  ...
};

[Peter Peterson]

(In [6928]) Adding the vast majority of atoms. Refs #1754.

[Peter Peterson]

(In [6930]) Removed the names of the elements from the struct and put in NAN everywhere that had wierd numbers. Refs #1754.

[Peter Peterson]

(In [6932]) Added an array for the elements so they can be searched for. Also moved nan to use the standard include statement. Refs #1754.

[Peter Peterson]

(In [6933]) Added comments to the code. Refs #1754.

[Russell Taylor]

(In [6935]) Fix for Windows. Re #1754.

[Peter Peterson]

(In [6958]) Put in the factory method and a test for it. Fixes #1754.

[Peter Peterson]

The build server doesn't seem to like the way I did things.

[Peter Peterson]

(In [6959]) Trying to get the tests to run on the build server. Refs #1754.

[Peter Peterson]

(In [6979]) Messed with the namespace in order to get the tests working. Fixes #1754.

[Peter Peterson]

(In [6981]) Trying again to make windoze happy. Refs #1754.

[Peter Peterson]

It looks like the build server finally likes my code.

[Janik Zikovsky]

All looks good, though I did not double-check every value in the table :)

[Stuart Campbell]

This ticket has been transferred to github issue ​2601