[2/4] git commit: WICKET-5531 Create new placeholder tag to indicate where header contributions should appear

WICKET-5531 Create new placeholder tag to indicate where header contributions should appear Add containers for to the HtmlHeader(Items)Container in the page (cherry picked from commit c31f30f6914b5d9bd146864015d5aebe16cd681c) Project: http://git-wip-us.apache.org/repos/asf/wicket/repo Commit:

[2/4] git commit: WICKET-5531 Create new placeholder tag to indicate where header contributions should appear

WICKET-5531 Create new placeholder tag to indicate where header contributions should appear Add containers for to the HtmlHeader(Items)Container in the page Project: http://git-wip-us.apache.org/repos/asf/wicket/repo Commit: http://git-wip-us.apache.org/repos/asf/wicket/commit/c31f30f6 Tree: h