A function to match gradeable steps

[Meratyn]

Match the gradeable steps in student's answer to gradeable steps in model answer.

Prerequisite: Aalto-LeTech/jsav-exercise-recorder#46

For now, this function should be similar to the one that JSAV uses with grading student's answer (JSAV "default grader").

Informally:

• begin from first step in student's answer and first step in model answer
• skip steps in student's answer until a gradeable step is encountered
• skip steps in model answer until a gradeable step is encountered
• if current steps match, increase score by one, then step forward one step in student's and model answer
• otherwise end matching

Functionality:

• add into JAAL data: ['animation'][i]['modelStep']' a _step reference_: what is the location of this step in the model answer: step hierarchy location major & minor step as array of integers. E.g. minor index 2 in major step 1 would be [1, 2]`
• the same from model step answers to student's answer