Updated assessment from walk through
Work in progress

This should filter the assessmentComponents to only handle question types.
On-going work for assessment extension

There are several changes in this commit:
- Handles new _assessment JSON format
- Calculation of score, max score and score as a percentage
- Tidied up formatting of messages and support for placeholders
- Optional score banding message
- Trigger to raise feedback when the assessment has been completed
Added code to handle percentages and pass scores

This is dependent on two attributes in the articles.json
- _isPercentageBased
- _scoreToPass
Updated README file and added sample JSON

Updated the following files:
- README.md
- example.json
Slight re-work and bug fix for max score

Fixed issue with the max score which had been relying on _score rather
than _questionWeight.

Also re-worked the JSON to remove the underscore character from
translatable attributes.
Minor text changes to documentation and bower.json
Adding tests
Merge pull request #1 from adaptlearning/feature/8928

Feature/8928