plan ignores added / removed

[hsmade]

Description

When a change in a nomad file adds or removes a stanza, levant plan ignores the change. This is particularly dangerous when you have a change in a template stanza, where any 'edit' translates into a remove and add of the whole stanza, instead of an edit (this is a nomad API thing). This happens because the code focusses on edits here: https://github.com/jrasell/levant/blob/master/levant/plan.go#L137

I'm more than happy to do a PR to fix this, but it seems like this was a conscious decision. So what are your thoughts on this?