Calligra Plan Qt6

[Carl Schwan]

Hi,

Now what the main Calligra is ported to Qt6, I would like to start doing the 
same with the Calligra Plan repo. To not duplicate porting work, I wonder if 
moving the Calligra Plan repo back to the main Calligra repo would make sense.

>From a quick look, various internal libs seems to be duplicated in the src/
libs folder of calligraplan.

Any opinion on this?

Cheers,
Carl