Revisit language on static props

[ghost]

From @justinfagnani

Re: properties like template and properties

We always call them the "static X getter", but really, a getter is just one way to implement
the property.

You could also just set the property on the constructor:

class MyElement {}
MyElement.template = html`...`;

Or if using a compiler, and in the near future in native JS, declare a static property:

class MyElement {
  static template = html`...`;
}