Bug with locale settings interfering with date ranges

[CalumMortimer]

Hi, great calendar. I have discovered a bug with locale while using the examples.

My "endDate" attribute of a current event is stored as "Thu Apr 01 2021 00:00:00 GMT+0100 (British Summer Time)" - probably based on my computer settings.

When displaying the "toISOString()" within the Modal, this converts to "2021-03-31T23:00:00.000Z"

Therefore, the Modal date range will be short by one day in both start and end date when updating the event. I suspect this will happen everywhere the locale time is set to UTC + x hours. So everywhere in the East half of the world.

The Calendar class should ignore locale settings completely and process dates in UTC only.