Cleanup database relationships, add trends view and test summary/details views

[trey-ivy]

This PR starts adding options to explore build metrics across all invocations.

Trends

It adds a trends view, which displays data for all invocation durations

and plans are to add a few additional visualizations to this view.

And it also adds a couple new views for tests.

Tests Summary

A searchable grid of all your unique test targets.

paginated for larger data sets.
expanding rows provides a link to the most recent runs. you can click the buttons and navigate straight to each invocation

Test Details

Provides more data and a further lookback period, and also a graph of duration over time so you can see if tests suddenly start taking longer to run to help spot regressions.

again, plans to expand on this view with further visualizations in the future.

Database Relationships

Also as mentioned in #11 there are several database relationships that need attention. This PR addresses everything I could find there. Additionally it extends the custom resolvers to add some queries used for exploring test data and stubs out a few methods for doing something similar for target data in the future.

Branding

I've also added a few options for branding. if you optionally include a company name and/or slack channel environment variables they'll be displayed in the header, footer and title page.

Other Minor updates

• sort invocations table by most recent first
• link tests to their given overviews on the invocation page/ tests tab
• nil checking for cancelled invocations

[mortenmj]

lgtm