XWIKI-10845: Provide an UI for managing Flamingo Themes.

(cherry picked from commit e6a5dded57079864dbb6714bba5ef0daae27812f)
XWIKI-10845: Provide an UI for managing Flamingo Themes.

(cherry picked from commit 115a75acb2e21121360b7727fae7ca250d82784e)
XWIKI-10845: Provide an UI for managing Flamingo Themes.

(cherry picked from commit 1cac6eb9055266bec254cd84df3b1a01cbebf42a)
XWIKI-10845: Provide an UI for managing Flamingo Themes.

* Hide the FlamingoTheme space by default, we could still access to the application via the administration (as before).

(cherry picked from commit 3f5b7f974f21364217f547bb0769c71eebcb9997)
XWIKI-10844: "Manage color theme" links to the old Color Theme Application.

(cherry picked from commit 38f794994a33bc1cdbfca3bc7909bd7ff9114afe)