Use mobi_bypass URL param, including on JSON feeds

Transition from using the nomobi URL argument to using mobi_bypass
(which seems to work with more regular success).

Also begin using mobi_bypass on JSON feed URLs, in a belt and
suspenders strategy to help avoid future issues with mobile
redirection.

Signed-off-by: Jeff Godin <jgodin@tadl.org>
Open Facebook links in external browser

Using the same technique we're using elsewhere, have links from the
Facebook feed open in the user's preferred external browser.

Signed-off-by: Jeff Godin <jgodin@tadl.org>