WL#2877: Triggers: store trigger metadata in tables

Triggers should be stored in tables.

Note: Monty agrees with this provided triggers
are also in the .frm. Details need to be worked
out.

During Roadmap discussions at the Heidelberg Dev Meeting,
Kostja committed to having an approved HLS for this
functionality by the time MySQL 6.1 enters beta. The
stretch goal is to have an approved LLD at the same time,
or shortly thereafter.