Optional moment.js Part 1

[prayerslayer]

Part 1 of #382

• Moves all calls on moment or instances of moment into date_utils. (That I found, at least. Since most date properties are still instances of moment I might have missed some.)
• Discussable if there are too many functions and how the moment-agnostic Date API should look like.
• No efforts regarding order of functions were made, this I'll do later but I still wanted to give you the change to look at it.

After this PR I would work on replacing the actual moment instances.

[codecov]

Codecov Report

Merging #1046 into master will increase coverage by 1.83%.
The diff coverage is 96.89%.

@@            Coverage Diff            @@
##           master   #1046      +/-   ##
=========================================
+ Coverage   81.27%   83.1%   +1.83%     
=========================================
  Files          13      13              
  Lines         721     817      +96     
  Branches      142     141       -1     
=========================================
+ Hits          586     679      +93     
  Misses         33      33              
- Partials      102     105       +3

Impacted Files	Coverage Δ
src/year_dropdown.jsx	87.8% <100%> (+0.62%)	⬆️
src/month.jsx	81.25% <100%> (-0.57%)	⬇️
src/week.jsx	72.72% <100%> (-0.61%)	⬇️
src/calendar.jsx	83.6% <100%> (-0.53%)	⬇️
src/month_dropdown.jsx	85% <100%> (-2.18%)	⬇️
src/day.jsx	87.64% <66.66%> (+0.43%)	⬆️
src/time.jsx	52.27% <88.88%> (-2.28%)	⬇️
src/datepicker.jsx	90.39% <94.73%> (+0.77%)	⬆️
src/date_utils.js	91.44% <99%> (+11.78%)	⬆️
... and 7 more

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[martijnrusschen]

Looks good, would be good if someone else could take a look as well.

[aij]

Looks good to me too.

I don't think we could completely remove moment while maintaining backwards compatibility, but we could probably make it an optional dependency.

[prayerslayer]

I don't think we could completely remove moment while maintaining backwards compatibility

Yeah me neither, unless you'd distribute separate builds for versions with and without moment. If that's not an option we'd need a flag somewhere to know which date utils to use and, as you say, moment as an optional dependency.

[prayerslayer]

Any idea what could be wrong with the failing test? It seems to be occuring also on master (see this build https://travis-ci.org/prayerslayer/react-datepicker/builds/281940187), so I assume it's a dependency issue?

I'll continue on a branch based on this PR instead of master.

[aij]

@prayerslayer It appears to be a fragile test. It looks like it will always fail on the first 2 days of the month.

[montogeek]

Any updates on this?

[prayerslayer]

@montogeek There's this #1327, but it's quite old by now, and has some blocking open questions.