Currently, the home page has a hard-coded summary panel specifically
for displaying overviews of subunit artifacts, which makes it
impossible to show information on other types of artifacts. This adds
a new 'summaryService' and associated 'artifact-summary' directive
that can dynamically create summary panels depending on artifact type.
Additionally, since the summary service allows many summary panels per
type per named artifact, we can have multiple (priority-ordered)
panels for each artifact. As an example of this, the existing subunit
summary has been split into simpler 'subunit-summary' and
'subunit-errors' panels.
Change-Id: I0d075dfcb86c6aef8c697896d1728e970b62600f
b2fedac4fe