Favor delegation over composition

* Renaming FlowOwnerView to ScreenConductor. It's not a specific view anymore (frame layout or whatever) and could be reused for any kind of container. This enables easily using several flow owners.
* Introducing CanShowScreen which has to be implemented by the flow view. Most likely you'll just want to delegate to a ScreenConductor, but you could also do your own thing.
* DemoActivity directly accesses the main flow instead of the boilerplate calls to up / back (with different names each time)
* Got rid of the weird retrieval code for MainView. Don't do this.
Child scope created during register() get state

Fix for #53.

When requiring a child scope, we only skip calling onCreate() on the child scope if we are in an onCreate() loading.
Merge pull request #54 from square/py/require_child_scope_in_register

Child scope created during register() get state
Merge pull request #49 from jaynewstrom/master

Update README
Merge pull request #40 from square/py/compose_flow_owner_view

Favor delegation over composition
Tweaks some confusing variable names in MortarActivityScopeTest
Debounces Presenter#onLoad, makes dropView more reliable.

Addresses https://github.com/square/mortar/issues/59.
Merge pull request #60 from square/ray/debounce

Ray/debounce
Update change log for 0.9
[maven-release-plugin] prepare release mortar-parent-0.9
[maven-release-plugin] prepare for next development iteration
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.
Merge pull request #64 from square/py/popup_presenter_name

Improving saving state of PopupPresenter
Makes Presenter#onDestroy call dropView
Merge pull request #65 from square/ray/drop-on-destroy

Makes Presenter#onDestroy call dropView
Update CHANGELOG for 0.10 release
[maven-release-plugin] prepare release mortar-parent-0.10
[maven-release-plugin] prepare for next development iteration
Alphabetize the Dev Scope ordering

Relying on the default ordering doesn't seem to jazz w/ Java 8.
Merge pull request #66 from holmes/holmes/alphabetize

Alphabetize the Dev Scope ordering