Content icon overrides

Users should be able to select from a list of icons for each piece of content. For example, instead of all Locations having the location icon (by default), users could select [house, road, river, mountain, etc] from a list of icons (from material icons) to use for that location in lists.

This would be for that particular location (or character, item, etc) instead of all Locations, Characters, Items, etc, and should replace the default icon for its class in lists wherever it's shown on the site (dashboard and the content/list partial).

Feedback:

>Changeable location icons. Cities, forests, rivers, etc. It would be easier to distinguish between locations if they all weren't mountain icons.

>Ability to add icons to your items, characters, etc.

Start by tracing how the dashboard and the content/list partial render default icons for locations, characters, and items. Review how each content type is represented, then determine where a per-content Material Icons choice would be stored and applied. Done means users can select an icon and see it replace the class default wherever that content appears.

Written by the indexing model from the issue text.