Fix ANR when retrieving cover art and add vector artwork

This MR includes two separate commits:

• A fix for a regression which is addressed by moving the call to retrieve remote artwork back to the IO thread pool
• An enhancement to incorporate vector art for three small notification icons (audio, video, scan)

Description

Regression only impacts 3.6.x branch. Refer to change in !1619 (merged) for modification.

Motivation and Context

Application deadlocks when loading RSS feed. Use xspf in note for testing.

How Has This Been Tested?

Tested on Pixel 3 running Android 11

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which cleans up / improves existing functionality)

Checklist

• I have read the CONTRIBUTING section of the README document.