webadmin: ISO/Export sub-tabs resizable columns

ISO/Export sub-tabs under Storage main-tab
now support resizable columns.

* Invoked enableColumnResizing() on each sub-tab.
* Added a static width value for each column.

Change-Id: Icf75b725fe9efa63c3e0a949c9d1bb9f6590d1aa
Signed-off-by: Daniel Erez <derez@redhat.com>