Convert UI to use icon font

[creesch]

The current icons belong to old reddit and don't really fit in new reddit. Probably also a good time to consider using a font based icon set so we don't have to mess with base64 blobs.

---

• Modbar icons
• Icon links in modsubs popup
• Buttons for manipulating lists/tables in the settings window (e.g. shortcuts list)
• Various places in the subreddit config dialog
• A whole ton of other stuff

[eritbh]

Per IRC, I'm gonna look into replacing the UI with Material icons. Reddit-specific stuff will be handled either with that or by stealing SVGs from Reddit, to be determined at a later date. For now I'll just put placeholders in for them.

[eritbh]

@creesch: I've added a to-do list to the top of this issue that's super incomplete, feel free to add to it if you want.

[creesch]

Modlog I already have an issue for and is seperate from this as far as I am concerned. Other than that it looks good.

[creesch]

This issue was moved to toolbox-team/reddit-moderator-toolbox#12