Remove MortarContextWrapper from the public API

```
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] Mortar (Parent) ................................... SUCCESS [0.739s]
[INFO] Mortar ............................................ SUCCESS [10.978s]
[INFO] Mortar Sample ..................................... SUCCESS [26.382s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 40.389s
[INFO] Finished at: Thu Dec 12 13:14:37 PST 2013
[INFO] Final Memory: 30M/81M
[INFO] ------------------------------------------------------------------------
```