Quality of life improvements to podcasts

[mbaiti]

gonic version: v0.16.4

if from docker, docker tag: sentriz/gonic:latest

First of all I love to use goinc 💛 following I have some improvements, especially to the Podcasts section:

1. Update the podcast cover on a regular basis
2. Ability to show different covers for each episode
3. More options for organising podcasts, e.g. #429