Fixed : CPDatePicker textual issues

This PR fixes several issues about the textual CPDatePicker :
- Fixed the issue about keyView loop when not assigning the nextKeyView
- Changed the behavior of the component when editing or deleting the date. It works as in cocoa now.
- Fixed bug about frameSize of each component when editing
- Fixed bug about NaN or null values
- Added optimization
- Refactoring the code
Fixed: issue with _dateWithTimeZone when timeZone is null

Fixed the private method _dateWithTimeZone when aTimeZone is null
Fixed: issues with timeZone

This PR fixes several issues with the timeZone.
It also changes the way to "calculate" the date of the textual datePicker.
Merge pull request #2052 from Dogild/CPDatePickerRefactor

Fixed : CPDatePicker textual issues