Remove Connectors from master build

[cgardens]

Child of #621

Tell us about the problem you're trying to solve

• We want the core airbyte master build to be fast and reliably green. As we add more integrations that will become impossible. Already we see some build flakiness due to all of the connectors (e.g. a failure in downloading deps for pip install).
  • Right now, for a commit that should pass the build there's only about a 66% chance that it does due to these transient failures.

Describe the solution you’d like

• The master build should be able to pass without building all integrations.
• Each connector should have its own build (that is triggered by the master build). The status of these builds should be displayed in the readme and docs.
• Includes manual (even CLI or UI) launching of an integration build for a branch.

[cgardens]

@jrhizor done?