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.