Time strings now converted correctly

- Removed all System.TimeSpan's
- Created a new Folder 'Utils'
- Created a new class 'TimeStringConverter' with two sub-classes
Earth-/KerbinTimeStringConverter

Fixes #192
Some small changes to the TimeStringconverter

- TimeStringConverter moved to SimpleTypes
- Utils folder removed
- KerbinDays are now 426 and not 365 and removed the const DaysPerYear
Merge pull request #206 from Peppie23/kerbin_time_timespan

Time strings now converted correctly