Finish editing of D7 core module page for Trigger

Split from Review and update D7 core module handbook pages

Need to address feedback from jhodgdon, comment #51 on the previously-mentioned page:

... reviewed http://drupal.org/documentation/modules/trigger and it is definitely closer, but I think it could still use a little bit of work:

a) Copy/style/capitalization/punctuation review - I saw a few things that needed fixing, nothing extremely major

b) Consistent terminology. In D7 at least, the events that cause actions to fire are called "triggers", not "events" or "trigger events" in the inline help. Let's use that terminology on this page too.

c) The Actions admin page in d7 is under Administration > Configuration > System > Actions

d) D7 developer section should also tell how to define actions (hook_action_info http://api.drupal.org/api/drupal/modules--system--system.api.php/functio...)

e) In D6 the tabs are not the names of modules. This needs to be made clear in this doc page, because as it reads now, it makes you think that "content" is a module name. It isn't. Also, is the "comment" tab called comment or comments?

f) d6 - Actions are not under Site building in the menu system, but actually under Site configuration.

g) See item (d) above - also applies to d6 where the hook doc is at http://api.drupal.org/api/drupal/developer--hooks--core.php/function/hoo...