webadmin: Implement validation in EntityModelCellTable

Validation accepts a list of errors, and outlines invalid entries
(ones which have non-empty errors) with a red outline, as well as adds
the invalidity reason as tooltip.

Change-Id: I8cddd3a6dbfe3cd9b18b631f4da13865b367d096
Bug-Url: https://bugzilla.redhat.com/1048752
Signed-off-by: Lior Vernia <lvernia@redhat.com>