Expand usage of HTTPS and fix a few URLs

README.md

clientgui/DlgAbout.cpp

clientgui/ProjectInfoPage.cpp

clientgui/SkinManager.cpp

clientgui/res/templates/skins/Resource Information.txt

clientgui/skins/Charity Engine/skin.xml

clientgui/skins/GridRepublic/skin.xml

clientgui/skins/People for a Smarter Planet/skin.xml

clientgui/skins/World Community Grid/skin.xml

doc/addon_item.php

doc/dg.php

doc/docutil.php

doc/download_all.php

doc/email_lists.php

doc/help.php

doc/help_lang.php

doc/index.php

doc/links.php

doc/logo.php

doc/manager_links.php