Populate max score when saving a Qualifying Test

[warrensearle]

When we save a qualifying test we should update the maxScore field for the test.

maxScore is the total available score for the test. It is calculated from the number of questions and the type of test as follows:

For Critical Analysis tests maxScore is the total number of questions. Users choose one answer per question and can therefore score 0 or 1 points per question. e.g. for a test with 20 questions the maxScore will be 20.

For Situational Judgement tests maxScore is twice the total number of questions. Users choose two answers per question, the 'most appropriate' and the 'least appropriate' answers and receive 1 point for each correct answer. Therefore there are two points per question. e.g. for a test with 20 questions the maxScore will be 40.

NOTE: Scenario tests are manually scored and we will handle this is future tickets... For now lets set maxScore to null for scenario tests.