Nerd Font Icon Support

**Is your feature request related to a problem? Please describe.**
I'd like to add the ability to customize GUI icons using nerd font.

**Describe the solution you'd like**
Add configuration options to the `yaml` file that allows you to update the icons with string definitions.

**Additional context**
I'm happy to code this myself, just need some help learning the project's folder structure.

Here's a quick idea of what I want to update (from my `gitmux` page)