Add unit tests for logic in client

[CBielstein]

There are several existing methods in the client project that could and probably should be united tested.

• DateTimeExtensions.cs
• DateTimeOffsetExtensions.cs
• PositionExtensions.cs

Potentially more. These don't have tests yet, but they should be added to find any bugs and protect against regressions.

[CBielstein]

Should include testing the new ReportList.cs and scenarios like #37.