Create FixModel and FixCollection classes

[n8rzz]

A class that defines a Fix and a collection of Fix instances. A fix is defined as a named point in geographical space. A fix may be part of StandardRoute, and may be used as a Waypoint within a StandardRoute.
note: StandardRoute and Waypoint are potential future classes

• Possibly extend the PositionModel class and provide utility methods for reasoning about a fix.
• Provide an interface for determining if a Fix belongs to a SID, a STAR, is an IAP, etc
• Via the collection, provide methods for filtering a fix based on current properties
• Update the CanvasController to use the FixCollection for rendering all or specific fixes based on conditions.

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This is a step towards allowing display of only SIDS or only STARS. And will provide a way to abstract fix-centric logic being done ad-hoc throughout the application.

[n8rzz]

depends on #19 & #35

this feature branch is off of #19 and not develop.

[n8rzz]

• create FixCollection
• add tests for FixCollection
• create FixModel
• add tests for FixModel
• updates implementations where possible