use https image urls when horde runs in https environment

this fixes bug #9983 from bugs.horde.org

now that the response of the api includes also an https url this should be used for https sites
Update index.php

$GLOBALS['browser']->usingSSLConnection() instead of $_SERVER['HTTPS']
Fix links
Revert "Fix links"

This reverts commit 1af205721e13864cca96a42b2b6171152b54d2af.
Fix links correctly.
explode() -> implode()
PEAR can only handle one extends tag
[mms] Add Horde_ListHeaders#headers().
Horde_Mime_Headers#listHeaders() is deprecated
Merge branch 'master' into imp_6_2