t. classProperty should allow to create static class property

t. classProperty should allow to create static class property e.g.

```js
t.classProperty(key, value, typeAnnotation, decorators, computed, static);
```
or
```js
t.classStaticProperty(key, value, typeAnnotation, decorators, computed)
```
that will help to create plugins that efficiently work with babel decorators plugin that simpy ignores good old ```ClassName.prop = 1``` notation.