Added elements to comply with PSP-1 Podcast RSS Standard

[endkb]

Added required XML namespaces that were missing:

• xmlns:podcast="https://podcastindex.org/namespace/1.0"
• xmlns:atom="http://www.w3.org/2005/Atom"
• xmlns:content="http://purl.org/rss/1.0/modules/content/"

Added required <atom:link> element. Attribute href is set by new PodcastFeedURL options in the profile template.

Converted <itunes:block> to <podcast:block> and added ability to specify blocks and allows for specific services in line with the PSP-1 standard. The Block option in the profile template can look like this: Block=[yes/no],[service]:[yes/no],[service]:[yes/no]