Eliminate character boolean fields

[danieldesira]

1. Eliminate character boolean fields
2. Create abstract and interfaces folder under characters
3. Create interface IMainCharacter.ts and declare methods unique to Turtle class

[danieldesira]

Need to delete _isSolitary field next. Probably, the best approach would be to declare a new abstract class named PackPrey with custom logic for initial positioning and swimming, which could then be extended by the Sardine class and any other future characters of this kind.

[danieldesira]

Refactoring complete.

[danieldesira]

We can improve this further as some properties that are declared in characters are not required for that specific character type.

[danieldesira]

Should be able to merge this with master and close the ticket safely.