chore: Replace moment.js by date-fns

[machour]

As mentionned in #523, we are currently using moment/min/moment-with-locales.min which weights 289.5K (63.8K) only to output the time ago information.

Even "worse", we don't even use the locales from the library for the translations, instead, we override them with our own wordings.

@ocarreterom proposed we switch to date-fns which is kind of a lodash for date handling, and will have a wayyyy smaller footprint, he will be working on the PR for this change 🎉

/cc @lex111

[ocarreterom]

@machour there is a problem. date-fns doesn't provide format translations for all the languages git-point supports.
distanceInWords, distanceInWordsStrict and distanceInWordsToNow always returns de units in words. I can't format as 1h.

It's a problem?

[machour]

yes, we definitely need those.
if you check our translations, we have a common.relative object with all the strings we currently display.

Looking at date-fns, it seems possible to adapt it our way:

var distanceInWords = require('date-fns/distance_in_words')
// Require Esperanto locale
var eoLocale = require('date-fns/locale/eo')

var result = distanceInWords(
  new Date(2016, 7, 1),
  new Date(2015, 0, 1),
  {locale: eoLocale} // Pass the locale as an option
)

Seems to me like we just need to mimic the eoLocale object and override its formatDistance property with our own definition.

https://github.com/date-fns/date-fns/blob/master/src/locale/eo/_lib/formatDistance/index.js

[ocarreterom]

OK.
This works, but we need to change the translations of relativeTime.

relativeTime: {
  lessThanXSeconds: {
    one: 'less than a second',
    other: 'less than {{count}} seconds'
  },
  xSeconds: {
    one: '1 second',
    other: '{{count}} seconds'
  },
  // ...
}

[machour]

Done \o/ Thank you again @ocarreterom !! 🎉