Implements a simple buildspec construction for morphs

Implements a simple buildspec construction for morphs.

A spec can be generated from a morph with

```js
morph.buildSpec();
```

The result of this is a JSON-like object. For a simple rectangle this
produces:

```json
{
  "_ClipMode" : "visible",
  "_Extent" : "<eval>lively.pt(100.0,100.0)",
  "_Position" : "<eval>lively.pt(38.0,514.0)",
  "_Rotation" : 0,
  "_Scale" : 1,
  "className" : "lively.morphic.Box",
  "droppingEnabled" : true,
  "halosEnabled" : true,
  "name" : "Rectangle1",
  "showsHalos" : false,
  "sourceModule" : "lively.morphic.Core",
  "submorphs" : []
}
```

To create a morph from a spec use

```js
morph = lively.morphic.Morph.fromSpec(spec);
```