webadmin: fixing buttons text misalignment

Removed redundant 'margin-right:3px' from dialogButton template.
* Causing an horizontal misalignment in text position
  on OK/Cancel/Close buttons. I.e. text is not aligned to center.
* Checked on FF/Chorme/IE.

Change-Id: I4a00915b9521e5c2d14dca97e57e8495e4ae6f90
Signed-off-by: Daniel Erez <derez@redhat.com>