[webui] forward linkrev and olinkrev to cmd=diff action

The webui's inner links always had linkrev=base, but it didn't care
[webui] display packages in tabs

In project/show we now open a 2nd tab if packages are inherited through
project links. Later on we might want to link from inherited packages
to another action, that only shows build results and not the inherited
package
[webui] fix test cases for inherited packages tab