Documentation for CATcher's parser

[cheehongw]

Is your feature request related to a problem? Please describe.
The codebase for CATcher's parser is not very well documented.

This refers to the models and section parsers found under src\app\core\models\templates. For example, when looking through tester-response-section-parser.model.ts, it is not immediately obvious what some of the functions such as buildExtractResponseParser(category: string), buildTesterResponseParser does.

Furthermore, the TesterResponseSectionParser, DuplicateSectionParser, etc all give a somewhat vague idea of what it is expected to parse, but there is no concrete example of the section it is parsing.

Describe the solution you'd like
Documentation for some of the above parsers and helper methods under src\app\core\models\templates.