Integrate Datez

[Mazyod]

I would like to propose integrating Datez into the app for simpler date calculations. Calculations from the legacy codebase use hard coded integers, which fails in case DST kicks in. In general, it's best to use NSCalendar APIs to calculate dates.

If we agree to integrate it, we probably would need to integrate Cocoapods as well, since it's the easiest way to keep the dependency in check.

@z3bi thoughts?

[z3bi]

We should definitely use the NSCalendar and NSDateComponents API to do all date manipulation. Datez seems like a convenient wrapper around those existing frameworks and makes it more concise to do the kind things we need. Sounds good to me. I would also agree about using Cocoapods.