header.php: some corrections & improvements
header.php: some corrections & improvements

pull dropdown-menu always to right side
changed <!-- Update alerts --> to <!-- Version Infos --> (just like it is in footer)
hide version infos in dropdown-menu if it gets shown in footer
repaired update-urls, they also should open up in new tab & gets underlined on hover
`background:none` is needed because AdminLTE adds dark bg on hover to links when using it on smallscreen (xs)
jacobsalmela/AdminLTE,jacobsalmela/AdminLTE,jacobsalmela/AdminLTE,jacobsalmela/AdminLTE