Finish coding data model classes and database accessor singleton class.

[identity2]

• Added data model classes: Answer, Question, Avatar, Accessory, so the database accessor singleton could communicate better with controller code.
• Implemented database accessor singleton to handle all database calls. Replaced the original database accessing code in controllers with single function calls to DatabaseAccessor. (Simply put, separated model code from controller code).
• Changed orientation from portrait to landscape. Adjusted views to adapt to landscape orientation.
• Deleted unneeded database "Choices.sqlite".

(Issue #70 Fixed)

[sunjunkie]

You should use the simpler Swift 3 pattern for singleton classes:

class ClassName {
static let sharedInstance = ClassName()
private init() {...}
}

then access the singleton : ClassName.sharedInstance.somefunc()

And then you don't need to check for whether the instance is nil.

[identity2]

@sunjunkie , I finished modifying the singleton class! :)

[sunjunkie]

There are still several instances of DatabaseAccessor.sharedInstance() so the project does not compile. (need to remove parentheses)

[identity2]

Oops, not sure why I did not compile the class for testing in the first place.
The compiler errors are all fixed now.