Fixes rotation in sample app. Revealed necessary API changes.

1. Drops Mortar#createRootActivityScope. It's really not practical for the
root scope to be an instance of MortarActivityScope, there's no sane way for
them to survive the life cycle without a parent scope in the Application.

2. Views are now required to call Presenter#dropView at the appropriate time.

3. In the sample, ContainerView replaced by a more convincing FlowOwner
(abstract presenter) and FlowOwnerView (abstract view).
Use ActionBarSherlock to make sample app work on Gingerbread.
Use flow-0.3 in sample, not a snapshot
Javadoc tweak on Presenter#dropView
Merge pull request #24 from square/ray/derp

Fixes rotation in sample app. Revealed necessary API changes.

```
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] Mortar (Parent) ................................... SUCCESS [0.442s]
[INFO] Mortar ............................................ SUCCESS [7.221s]
[INFO] Mortar Sample ..................................... SUCCESS [22.987s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
```