Add primary key index to LayoutGroup DTO and add ProvidesKey to CellTable.

Add primary key index to LayoutGroup DTO and add ProvidesKey to CellTable.

This allows the primary key to be retrieved by the Details button. This
functionality has not been implemented yet but it's in the works.

* src/main/java/org/glom/web/client/activity/ListActivity.java: Pass
the LayoutGroup result to ListView.setCellTable instead of all of its
fields individually.
* src/main/java/org/glom/web/client/ui/ListView.java:
* src/main/java/org/glom/web/client/ui/ListViewImpl.java: Use
LayoutGroup as parameter for setCellTable. Add ProvidesKey to CellTable
get the primary key for the table.
* src/main/java/org/glom/web/server/OnlineGlomServiceImpl.java: Set the
index of the primary key in the LayoutGroup accounting for hidden
primary keys. Rename getJavaNumberFormat() to
convertToJavaNumberFormat() for consistency. Cleanup / add some
comments.
* src/main/java/org/glom/web/shared/layout/LayoutGroup.java: Add a
field for primary key index and a field to indicate whether the
primary key is hidden or not.