gconfig: enable rules hint for main treeviews

Due to the large amount of rows in the treeviews, is difficult to
match columns with rows, setting the rules hint to 'true' allows the
treeview to alternate background colors in the rows making the data
more readable.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Tested-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>