Improve installed usage

commit 105c7610:

meson: Fix pkgconfig file names
They should always be libfoo.pc

commit 6a83908c:

meson: Install headers for all libraries
Closes https://gitlab.freedesktop.org/gstreamer/meson-ports/ffmpeg/issues/7

commit d439191e:

meson: Add option to disable CLI
Matches the same option available with ./configure