coreos-download: fix inconsistent button and tab view
Fixes a bug that when users select a stream, the div section will be re-rendered into
default "Cloud Launchable" instead of the tab users selected, creating inconsistency
between tab button and tab view.
To reproduce, select a tab other than "Cloud Launchable", say "For Cloud Operators".
If we now select another stream, the div section below will be re-rendered with the
default "Cloud Launchable".
Also factors out the frequently used div IDs and deduplicates "toggleHidden" function.
Signed-off-by: Allen Bai <abai@redhat.com>