feature req: change offline calender to other type

[nutpantz]

I'm in the process of changing my calenders from Google to device only, and plan to run a server to sync to.
But i will not be building the server until next month and would like to make my calenders now.
(As i have time now and no money, later i will have money)

I need an option too switch an offline calendar to an online calender later.