feat(skeleton-loader): Create GlSkeletonLoader component

Created a skeleton loader component,
that will accept skeleton states and
apply a loading animation for our UI.

Update snapshots

Create pipeline row skeleton component

This commit creates the pipeline
row skeleton component that will
be used on the pipelines view.

Revert changes and add examples

Revert skeleton dir changes, we
need more testing on gitlab with
any components we think can be
reused. Added more examples to
the skeleton loader component.

Revert files prettier touched

Add more content to docs

Fix a typo in docs

Add docs and wrap examples in div

Add docs about progressive loading,
also wrap skeleton loader examples
in a div to ensure proper widths.

Update snapshots

Add warning message for empty slot

Avoid assignment and log message directly

Remove fill attributes from examples

Convert component to functional

Moved SFC into a functional
component for perf gains. Added
documetation for props.