Add tests of .getMoleculeAtoms()

[#61540920]
Implement .getMolculeAtoms() using iterative DFS instead of recursion

[#61540920]

It really speeds up models with large molecules (e.g. with proteins).
On desktop I can see that engine time is 4ms instead of 8ms, while
on iPad it's 14ms instead of 63ms! What results in FPS increase from
13 to 38.
Expose .addKEToAtoms() function in Scripting API

[#61549892]

It has been added recently to engine (during work on chemical
reactions) so it makes sense to make it available for authors too.
Add mocha tests of .addKEToAtoms() function

[#61549892]
Chemical Reactions: add curricular model for "Hydrogen-Oxygen Reaction"

[#61137184]
Chemical Reactions: add curricular version of "Hydrogen-Oxygen Reaction"

[#61137184]
ITSI: Activation Energy 1 interactive