IA Page - merge ia/view/<id> with ia/edit/<id>

@russellholt @jdorweiler @jbarrett 

It also performs user permissions check on page load, and, depending from the result, stashes the appropriate class to the Xslate template.
That class is then used in IAPage.js to assign the appropriate Handlebars template to the page.

I prefer keeping two separate Handlebars template for the same page because I feel it's less messy than adding/removing classes in the JS file.
Here you could do:

```perl
if ($c->user) {
    $permissions = $c->stash->{ia}->users->find($c->user->id);
}
```

Then you won't need that error condition