Stable release candidate 1.3.0-rc3

One more hopefully last pre-release as we work our way to 1.3.0 final. Thanks to everyone helping to test and fix things, especially @henrique-borba and @kk6mrp on this set of updates. Changes since RC2 below:

f12db8b0 fix layout of "stay logged in" option on login form                              (2021-06-28) <Jason Munro>
20d9a7ea remove obsolete log tag                                                          (2021-06-28) <Jason Munro>
db132836 Updated and fixed sent folder not configured warning                             (2021-06-28) <Henrique Borba>
6a8b5301 fix links to newer online docs                                                   (2021-06-14) <Jason Munro>
cce56e80 honor redirect_urls even if not an HTTP POST                                     (2021-06-14) <Jason Munro>
54f204a9 correct redirection when 'First page after login' is set                         (2021-06-12) <Weston Miller>
edb043a8 add github unseen support to highlighting, clean up some duplicate code          (2021-06-11) <Jason Munro>
537e5d09 add support for seen/unseen feed highlighting                                    (2021-06-11) <Jason Munro>

This is the last RC candidate to include new features. We should be ready for the final release after a few days of testing.