XWIKI-11299: On subwikis (using Flamingo), 'Administer Wiki' links to the 'import' action.
XWIKI-11304: Cannot use, in a subwiki, a skin based on Flamingo stored in the main wiki.
XWIKI-11302: Cannot use, in a subwiki, a skin stored in the main wiki and a color theme stored in the subwiki.
XWIKI-11292: Not rendered ColorTheme properties in Flamingo's CSS
XWIKI-11306: Breaking compatibility: applications that are using the <meta name="language"> do not work anymore.
Merge branch 'master' of github.com:xwiki/xwiki-platform into feature-tree