Closes #624 #573: i18n improvements

Added the SyncLang command

Auto generated lang files

Added the helper to convert array to string

Now the SyncLang command able to generate the correct lang file

Added the contribution guide into lang stub

Generated the csv file

Added additional media library sidebar translation

Configure vue-timeago to respect the set locale

Configure date-fns and flatpickr so they respect locale

Internationalize some frontend strings

Add a Polish translation of the frontend

Revert date formatting that's not working on php7.1

Internationalize emails

Internationalize some more email strings

Internationalize all remaining auth strings

Internationalize dialog strings

Internationalize block remove modal

Changed Update label back

Fixed a typo in lang/en

Added more Chinese translations

Update vue-timeago