Allow admins to remove CKAN flag

[HebaruSan]

Motivation

Currently the CKAN badge can't be removed from a mod even if the CKAN team decides not to add it to CKAN. This may confuse users who think it would be there and can't find it, and it also causes some minor unnecessary network traffic from SpaceDock to the CKAN webhooks when the mod is edited or updated.

Changes

Now admin users will see a new X button within the CKAN badge:

When you click it, a confirmation dialog appears:

If you click the Remove CKAN Flag button, then a new /mod/<mod_id>/unckan route removes the flag and refreshes the page so you can see the badge is gone.

Also the mod page's div.header previously had a background: transparent; style which was immediately overridden by background-color: #FFFFFF;. In practice all this accomplished was to mess up the layout of the header graphic. This is now removed so the header graphic will appear as it was intended to.

[DasSkelett]

SpaceDock/KerbalStuff/blueprints/mods.py

Lines 302 to 306 in 4dee33b

	if not ckan and mod.ckan:
	if not mod.published or newly_published or current_user.admin:
	# Allow unchecking the CKAN badge while the mod isn't published yet
	# or all the time for admins.
	mod.ckan = False

#337

?

[HebaruSan]

Oh, I forgot that! I thought we had a conversation recently about the need to add this.
Never mind!

[HebaruSan]

Will need to find a new home for the transparent side fix, though. #420 maybe.