Show async errata when a package

The async erratum column will be shown in the task view if at least one of the
packages has its 'errata' field with a value
Merge pull request #148 from thescouser89/show_async_errata

Show async errata when a package
Automatically add the 'Not Shipped' tag to packages

Automatically add the 'Not Shipped' tag to packages that are in the Not Shipped
list. The mead scheduler is probed to know if a package is in the 'Not Shipped'
list or not
Small optimization regarding to previous commit
Merge pull request #149 from thescouser89/automatic_not_shipped_tag

Automatic not shipped tag
Fix for NilClass in Tag
Merge pull request #150 from thescouser89/automatic_not_shipped_tag

Fix for NilClass in Tag