Switch to build-facts for consuming from other build servers

[cburgmer]

build-facts is a fork of buildviz retaining the logic to sync from other build servers. It has in the meantime gained more features, e.g. support for Concourse (some of the aspects not yet supported here though).

Let's specialise on the analysis and presentation in buildviz, while migrating the sync logic into build-facts.

Todo

• New release
• Update README
• Remove sync code
• Clean up Wiki
• Change hint on empty startup to use new endpoint
• Update docker support
• Think about retiring the old API or at least unify the JSON schema validation aspects