Improving saving state of PopupPresenter

Fix for #61: PopupPresenter shouldn't use a unique KEY.

* PopupPresenter saves the given popup info with a customizable key, so that several PopupPresenter instances can peacefully coexist side by side without fighting each other.
* PopupPresenter now also saves its popup instance state. E.g. if there's an input, this input should be preserved on rotations (and when leaving / coming back)
* Updated version to 0.10-SNAPSHOT due to non backward compatible changes: `Popup` interface requires implementing `onSaveInstanceState()` and `onRestoreInstanceState()`