Note to remember to structure feed subs later.
CREATE should UPDATE if post already exists.
Button to switch to new feed storage mode.

Resolves #152
set a post_meta with feedUrl
Making sure feedUrl is set.
Bypasses guid issue created by me...

...not properly understanding how guid assignment works. >.<
Merge remote-tracking branch 'origin/2.3.x' into 2.3.x-opml-subscribe