Add editor HTML element to plugin bindings

@stevermeister what do you think about passing the HTML element that hosts the editor in the bindings property of ngWigPlugin? In that way, we could overcome difficulties that appear when using multiple editors in a template and simplify the way to find in which editor the plugin belongs to.

For example, in clear-styles plugin, we use the following to find the actual editor element:

var ngWigElement = e.target.parentElement.parentElement.parentElement.parentElement.parentElement;
var container = angular.element(ngWigElement.querySelector('#ng-wig-editable'));

which is really error prone and difficult to read and test. It could be changed to something like:

var container = angular.element(this.hostElement);

[stevermeister]

let div = document.createElement('div')
div.innerHTML = ngModel;
ngModel = div.textContent

[bampakoa]

I really like your approach. Never thought of it! It is also much more testable. I will make the change and submit a PR for that. Thanks!