Clean up TileList css

For the TileList and TileListItems components, clean up the one-off CSS adjustments that are currently in use. Be systemic by replacing them with some custom spacing classes that currently live in custom-spacing.scss. There may also be ways to better leverage existing Vue and Buefy components. See the discussions in #75 for more info on how this has failed so far.

Also, if this cleanup can address the inconsistency noted in this screenshot from #82 that would be great: If anyone feels this is better addressed in a separate issue, that's fine, too.