Show the list of Tables and allow viewing (empty, for now) Details.

* app/src/main/java/org/glom/app/dummy/DummyContent.java:
  Replaced this with
* app/src/main/java/org/glom/app/TableListItem.java just so we
  have a toString() for the ArrayAdaptor to call, to get a
  human-readable title corresponding to our internal ID (table name).
* app/src/main/java/org/glom/app/TableDetailActivity.java:
* app/src/main/java/org/glom/app/TableListFragment.java:
  Add a shared based class:
  app/src/main/java/org/glom/app/DocumentActivity.java:
  that lets both activities accept the URI via the intent,
  with both activities parsing the XML document.
  This seems wasteful, but seems to be necessary to allow the
  activities to be independent.
* app/src/main/java/org/glom/app/TableDetailActivity.java:
  onCreate(): Get the provided table name from the intent.
  Add a callback to get the table title from the parent
  activity (which can be either the list or detail activity,
  depending on layout).