Use fontawesome icon for timeline zoom out, remove unused static files

[tw4l]

Fixes #876

Description

This fixes a problem where the path to a zoom out icon was hardcoded to /static by replacing that icon entirely with a fontawesome icon, consistent with the other icons in the Vue header.

Additionally, a few unused static images that are not being used in the app are removed.

Screenshots (if appropriate):

New fontawesome icon:

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.

[tw4l]

One more quick patch release change for you to review, @ikreymer :)

[Quirinus]

Thanks!