AM/PM - 12 hour time picker

[JamesMcIntosh]

Fixes issue #35

I have tested the code in time_picker_widget.dart

I ported the code from time_picker_widget.dart across into datetime_picker.dart

[JamesMcIntosh]

@radvansky-tomas I've updated my PR with code formatting and the couple of changes you made, I did notice that in your branch you reverted DateTimePickerWidget._changeMinuteSelection change which I think will now break when minutes are divided into intervals.

[rdev-software]

@JamesMcIntosh I am not aware of any revert, I simply took latest version and added AM/PM like you did, for my personal project. If there are any bugs / missing parts...feel free to fix / change that. Once I see that is merged and stable enough I will switch back from my fork ;)

[JamesMcIntosh]

Hi @dylanwuzh, just wondering if you are going to test/ review this pull request? I'm not actively using this library at the moment but and happy to finish getting this pull request merged into your source if you have any feedback.

[shadyshrif]

I don't know why such a feature isn't merged yet! I want it badly.

[jamesdixon]

@dylanwuzh LGTM :)

[rdev-software]

Sorry guys bit busy and sick lately. Feel free you use my codes, as I said before I am not aware of any reverts I did during dev. So test it and let me know if it broke something.

[shadyshrif]

For me, I used this lite plugin for time selection until that pull request is merged and the plugin is updated.

https://github.com/icemanbsi/flutter_time_picker_spinner

[JamesMcIntosh]

@dylanwuzh Are you going to merge this PR?