Add blockly modal function editor

Goals:
1. Hide function definition when not being edited
2. Improve discoverability of parameters
3. Improve discoverability of creation
4. Improve discoverability of edit

This change builds on the following WIP review:
[#244 [WIP for review] Support multiple top-level SVG Workspaces and Toolboxes](https://github.com/code-dot-org/code-dot-org/pull/244)

![screen shot 2014-11-03 at 4 10 51 pm](https://cloud.githubusercontent.com/assets/413693/4892812/70b6b96e-63b7-11e4-82ed-5790da63450a.png)
Hm, this method name / comment are pretty confusing:

`checkConnection`

```
   * @return {boolean} True if the search needs to continue: either the current
   *     connection's vertical distance from the other connection is less than
   *     the allowed radius, or if the connection is not compatible.
```

I imagine `less than the allowed radius` should be `greater than the allowed radius`?