Catch usages of "this" in bindings

Either by copy/paste or unintentional manual entry, I've caught myself a few times doing something like _this_...

```
<a href.bind="this.something.url">...</a>
              ^^^^
```

... instead of ...

```
<a href.bind="something.url">...</a>
```

It'd be great if the linter could find instances of `this` within bindings and throw a warning.