suggestion: change from feathericons to simpleicons

[KhaaL]

Since feather icons are not going to add more brand icons (see issue below), would it be feasible for this project to switch to another theme provider? E.g., icon theme for Mastodon won't be added which is a large social media site(s).

feathericons/feather#763

[v-shenoy]

Duplicate of #69