Properly create triggers with status other than the default "origin".

[martsberger]

The default status for a trigger is "origin" and the create_statement will create this type of trigger just fine. For the other three types "disabled", "replica", and "always" the create statement needs to be followed by an alter table statement setting the proper trigger type.

Fixes this issue in migra https://github.com/djrobstep/migra/issues/172

[djrobstep]

Hi there, thanks so much for submitting this PR, and sorry it's taken me a while to getting to review. All looks great apart from a couple of minor typos, I fixed them up and put them in a new PR here (https://github.com/djrobstep/schemainspect/pull/75) would you mind taking a look and confirming it looks fine and then I'll merge it!