Configureable min height width

I have a situation where I'd like to be able to have an editor smaller than 100px in height, but it's hard coded into the source.

Commit #  9a5e5a8291452ae962e9603ce426db5dc7ada290 should allow you to change that by setting:

```javascript
tinyMCE.Editor.MIN_HEIGHT = 75;
```

before calling

```javascript
tinyMCE.init({ height: 75, ... })
```