Slight modification to *Mapper comments.

Slight modification to *Mapper comments.

* src/main/java/org/glom/web/client/mvp/DataActivityMapper.java
(DataActivityMapper)
* src/main/java/org/glom/web/client/mvp/DocumentSelectionActivityMa
pper.java
* src/main/java/org/glom/web/client/mvp/TableSelectionActivityMappe
r.java
Remove comments mentioning GIN because they are just copied from
the example code and are apparently not helpful:
http://groups.google.com/group/google-web-toolkit/msg/82f0098b20669a73
Also change the mention of a class that is only in the example code.