Refactoring of section 3

[steve-crouch]

Taking into account PR #297, number of steps for refactoring:

1. Learning narrative changes - software design episode

   • move poor design choices and technical debt to after intro
   • make design goals understandability, testable, maintainable (as high-level concepts) then echo these high-level concepts throughout the intros to code refactoring and code abstractions
   • move architecture & MVC intro to after good software design goals, then include a discussion of how MVC relates to the high-level concetps of understandability, testability, maintainability
   • bringing software design episode techniques section up to level of design

2. Reordering of refactoring and abstraction episodes to follow better the narrative of design / abstraction / implementation (see PR Swap refactoring and abstractions episodes  #327)

   • exercises may need some work
   • highlight in episode introductions the high-level concepts

3. Update section intro to reflect the reordering and learning narrative changes

4. Verify changes w.r.t. Thomas' inflammation code repo updates

[anenadic]

Closed via #333