Get rid of calculations inside the date-io

The main idea is to resolve #279 Treeshaking issue. Right now we fully depend on the date libraries for calculation of something. But maybe will be a better idea to provide an interface only for localization-related features (like formatting, parsing, getting day ranges)

Problem: no way to get some specific functionality outside of date-io quickly. Need to get a patch. Also if some consumer of date-io is not using one of the methods - they will not be treeshaked

Solution: Provide a method for converting value back to js date object like `toJsDateObject` and use date-fns functions for consumers. This will not generate a lot of bundlesize for end-users, because functions like [this](https://github.com/date-fns/date-fns/blob/master/src/isSameHour/index.js) are really tiny. The most bloating part (formatting and parsing) we will not require anyway