web: Remove bar graph flicker by not recreating them

Don't recreate entire rows and cells and contents in the containers
and images tables. Just update the contents if a row already exists
for the container.

This allows us to simply update value="x/y" for the bar row div
rather than replacing it and causing animations all over the place.

Also simpler.

Fixes #320
Closes #331
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>