Calendar Import - Export (ics)

Invalid date

## 2.5
* Fix issues with both all day event export and import

## 2.4
* Automatically refresh calendar information when changed outside the app
* Suggest filenames when saving to reduce required typing
* Developer mode changes for debugging user issues

## 2.3
* Fix importing calendars from emails (thanks to Fred Dupont)
* Fix an exception when exporting on some systems
* Use Android 6 runtime permissions