* Rewrite _currentDate to work in all time zones
The method toISOString() returns a timestamp in UTC. Thus, midnight in the CET
timezone (UTC+1) was converted into yesterday@2300 and then that date was used
as the current date.
This made the logbook and history start with yesterday's data, at least for
locations east of UTC.
The new version avoids this by using methods that work in local time.
* Remove an embarrassing amount of lint
* Rewrite to be more concise
Proposed by @armills.
* Fix color picker
* Fix map panel CSS
* Convert logbook to use vaadin date picker
* Fix logbook clear date
* Migrate history panel to use vaadin date picker
* Remove pikaday
* Lint
* history panel: disable on loading
* Support multi-day history charts
* Fix lint
* Reduce the periods to 1/3/7 days.
* Switch to end_time param instead of days
* Move async waiting from history-data to panel-history
* Take navigator.languages into account when determining the preferred language
* Lookup language only once, use it also for other date/time functions
* Show the date picker value in localized date
* Show the date picker value in localized date (in history)
