Make glue and lal Recommended, but not hard dependencies

lal is used only for LIGOTimeGPS, and the import is at the point of
use and not at module level. glue is used to provide old ILWD format
support, and glue imports are guarded by if statements. The basic
functionality of python-ligo-lw is still present if lal and glue are
missing, so it is appopriate to describe the relationship using
`Recommends` rather than `Depends`.

On the other hand, LALSuite uses glue pervasively, so LALSuite must
Depend on python-ligo-lw.

This breaks the circular dependency that was a problem in
lscsoft/lalsuite!644.
3 jobs for lal-and-glue-recommmended-not-required in 2 minutes and 19 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #882013
build-python27

00:01:26

passed #882014
build-python37

00:00:47

 
  Docs
passed #882015
docs

00:00:53