calibre building gives warning
	CDBS WARNING:    DEB_DH_INSTALL_ARGS is deprecated since 0.4.85

switch to dh_python

Python3 -> experimental branch
Calibre4 -> master-4.0 branch
both -> python3-calibre4 branch

do not use dh_installman for all the 600 man pages, since it
recodes each and everyone from UTF-8 to UTF-8, eating billions
of CPU cycles, not really necessary, save the world!
