doc: add reference to full email address and purpose for lists Added purpose for lists to the mailing list table. Also added headers. Some grammar fixups. Promote WebChat IRC interface over client interface as many people don't have clients installed anymore 8-(. Added a sentence that guides the user to the address of the mailing list. I added this after getting an issue about a request that should have gone to the mailing list. I realised there was no reference to the mailing lists' domain: @lists.sourceforge.net on the contact page. I think the linked subscribe page used to provide a hint, but it doesn't look like it does anymore. I wonder if we should add a mailto: link there? Does sphinx obscure it enough to prevent bot spamming?

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