[DISCUSS] move quartz to grails-core

[James Daugherty]

We moved the other plugins to grails-core repo, but we did not do
Grails Quartz.  We recently had
https://github.com/apache/grails-quartz/issues/174 opened and it would
be easier to have the upgrade guide include these official
instructions / forge fixes.  What are people's thoughts about merging
this one too?