Add support for VEVENT QR code

[bertvandepoel]

As part of the physical promotion for the Open Source Job Fair, we were looking into how to make it more easy for those wishing to attend to save relevant information. We came across a standard practice to encode a VEVENT into a QR code.

Many existing QR apps correctly identify this format and give users the option to launch a calendar app to add the event in the QR code. Sadly, SecScanQR does not seem to have support for this feature yet. Could this feature be added or is this something for which we could submit a PR? We may be able to submit some code if you don't have the time to write this feature but are willing to review and merge it.

References:
https://github.com/zxing/zxing/wiki/Barcode-Contents#calendar-events
https://icalendar.org/iCalendar-RFC-5545/3-6-1-event-component.html

[bertvandepoel]

@Fr4gorSoftware is this an option that can be considered? Do you want to write it or are others free to write a PR?