Frontend - Added support for https artifact links

[Ark-kun]

Currently the Artifacts list makes artifact URLs clickable only when they are 'gs://'.
This commit adds support for https: links.

This change is 

[Bobgy]

Thanks for the try! It's a good start. : )

Some nitpickings only.

[Bobgy]

You need to take a look at Travis failure too. Some formatting warnings there.

Follow guide https://github.com/kubeflow/pipelines/tree/master/frontend#code-style for setting up automatic formatting in IDE. Or run a command to format.

[Ark-kun]

You need to take a look at Travis failure too. Some formatting warnings there.

Follow guide https://github.com/kubeflow/pipelines/tree/master/frontend#code-style for setting up automatic formatting in IDE. Or run a command to format.

Done. Thanks.

[Ark-kun]

I've decided to rename GcsLink to ArtifactLink since it's no longer GCS-only.

[Bobgy]

@Ark-kun Thanks, this looks great!

I didn't add unit tests initially, so let's skip them this time. The changes are simple enough.

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Bobgy

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[Bobgy]

/retest

[Ark-kun]

/retest