Add icons to page headers + subscription tabs

[ChunkyProgrammer]

Add icons to page headers + subscription tabs

Pull Request Type

• [x] Feature Implementation

Related issue

closes https://github.com/FreeTubeApp/FreeTube/issues/6267

Description

Adds icons to page headers when it makes sense to do so + adds some icons to subscription tabs (similar to trending tabs)

Screenshots

Testing

• go to pages: subscriptions, subscribed channels, settings, user playlists, history, about (Most Popular was updated as well but I'm not aware of any public instances with api enabled + most popular enabled)
• see new icons

Desktop

• OS: Fedore Linux
• OS Version: 41 KDE
• FreeTube version: latest nightly