Display the correct number of data items in the pager.

Display the correct number of data items in the pager.

This commit fixes:

https://bugzilla.gnome.org/show_bug.cgi?id=661441

* src/main/java/org/glom/web/client/ui/list/ListViewTable.java:
* src/main/java/org/glom/web/client/ui/details/RelatedListTable.java:
The implementation is the same for both tables: Keep track of the
number of non-empty rows and fire and RowCountChangeEvent after the data has
been updated.
* src/main/java/org/glom/web/client/ui/list/ListTable.java: Add a
custom Pager class that subclasses SimplePager to handle displaying
the correct number when empty rows have been added.