Start moving the existing OnlineGlom code to MVP.

Start moving the existing OnlineGlom code to MVP.

This work is based on the GWT MVP framework that is documented here:

https://code.google.com/webtoolkit/doc/2.2/DevGuideMvpActivitiesAndPlaces.html

This is the third commit of a refactor that will allow OnlineGlom to
be used with multiple documents.

* src/main/java/org/glom/web/client/ClientFactory.java: New file.
Interface for client factory which is used to get instances of various
classes throughout the app.
* src/main/java/org/glom/web/client/ClientFactoryImpl.java: New file.
Implementation of client factory.
* src/main/java/org/glom/web/client/OnlineGlom.java: Add code to
initialize the MVP framework.
* src/main/java/org/glom/web/client/activity/OnlineGlomActivity.java:
New file. Activity manager for the main container widget. This is the
Presenter in MVP.
* src/main/java/org/glom/web/client/mvp/AppActivityMapper.java: New file.
Maps place (URL) to its corresponding activity.
* src/main/java/org/glom/web/client/mvp/AppPlaceHistoryMapper.java:
New file. This is just a place holder for a generated file.
* src/main/java/org/glom/web/client/place/OnlineGlomPlace.java:
New file. Represents the URL for the main Online Glom app.
* src/main/java/org/glom/web/client/ui/LayoutListView.java: Update
for changes in LayoutListViewImpl.
* src/main/java/org/glom/web/client/ui/OnlineGlomView.java: Create
interface for View. Move code to OnlineGlomViewImpl class.
* src/main/java/org/glom/web/client/ui/OnlineGlomViewImpl.java: New
file. Implementation of OnlineGlomView.
* src/main/resources/org/glom/web/OnlineGlom.gwt.xml: Add Activity and
Place resources. Use ClientFactoryImpl by default.