move all fusiondirectory dev manual into a fusiondirectory subidrectory

hello,

like we have done in the user manual, we should move all fusiondirectory dev instructions into a fusiondirectory subdirectory

Cheers

changed milestone to %FusionDirectory 1.3.1

added PJ2003-0343 label

mentioned in commit 35f516dd

mentioned in commit 31fd2100

added 30m of time spent at 2020-12-16

added Changed label