[AndyB] Feed export 2.0

Title in option page is now optional as it defaults to board title.

Now removes lightbox code when first image is using the IMG tag.

First post message quotes are now removed.

• Fixed issue with thread prefixes.

• Fixed issue if first post message returns null.

Feed export v1.4 changes:

• Updated snippet code. Added thread prefix support.

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Now supports showing a single thumbnail image in feed description.