REQUEST: downgrade 'No Aurelia APIs are defined for the element: "xxx".' from thrown error to warning message

**I'm submitting a feature request**

currently aurelia enhance is falling over when it gets elements with element/controller/view-model/view which are not defined

and it breaks the bootstraping of aurelia

caused by this code

```
function getAU(element) {
let au = element.au;

if (au === undefined) {
throw new Error(`No Aurelia APIs are defined for the element: "${element.tagName}".`);
}

return au;
}
node_modules\aurelia-binding\dist\aurelia-binding.js
```

is there any chance this could be sent as a warning or try/catched into a warning

currently monkey patched with this in dev which not ideal, to stopping html inserted ahead of js components being deployed breaking builds

```
// Monkey Patch : turn thrown error into error message
import {NameExpression} from 'aurelia-binding';
function getAU(element) {
var au = element.au;

if (au === undefined) {
// assumption that aurelia instance available
aurelia.logger.error('No Aurelia APIs are defined for the element: "' + element.tagName + '".');
// throw new Error('No Aurelia APIs are defined for the element: "' + element.tagName + '".');
}
return au;
}
NameExpression.locateAPI = function locateAPI(element, apiName) {
switch (apiName) {
case 'element':
return element;
case 'controller':
return getAU(element).controller;
case 'view-model':
return getAU(element).controller.viewModel;
case 'view':
return getAU(element).controller.view;
default:
var target = getAU(element)[apiName];

if (target === undefined) {
throw new Error('Attempted to reference "' + apiName + '", but it was not found amongst the target\'s API.');
}

return target.viewModel;
}
};
```

* **Library Version:**
ALL

**Please tell us about your environment:**
* **Operating System:**
NA

* **Node Version:**
NA

* **JSPM OR Webpack AND Version**
NA

* **Browser:**
NA

* **Language:**
NA

**Current behavior:**

**Expected/desired behavior:**

* **What is the expected behavior?**
Aurelia should be robust and not fall over / aka cascade exception, when finding dom without Aurelia API

* **What is the motivation / use case for changing the behavior?**
Aurelia should be tough and handle not ideal html gracefully (but still call out error and the situations)

Start with getAU and NameExpression.locateAPI in the referenced node_modules/aurelia-binding/dist/aurelia-binding.js. Trace how missing Aurelia APIs during enhance affect bootstraping, and determine the expected warning behavior from the issue's monkey patch. Done means missing APIs no longer cascade into a thrown error while the situation is still reported.

Written by the indexing model from the issue text.