Abstract position calculation from PositionModel to helper function

[n8rzz]

There are many spots within the app that use the PositionModel just to obtain coordinates. If the method for calculating those coordinates were abstracted, we could skip the step of creating a model and get right to the data we actually need.

• move positon to a getter
• move gps to a getter
• abstract .distantceToPoint()
• add tests for .distantceToPoint()
• abstract position -> coordinate calculations
• add tests for newly abstracted function
• update implementations of PositionModels that are using only the coordinates to use new function