WICKET-5392 Responses for package resources cannot be compressed

Do not flush the response after writing the headers for a resource.
This was needed as a workaround for some old version of Firefox.
WICKET-4997: render bookmarkable urls for bookmarkable pages (not stateless)

Conflicts:
	wicket-core/src/main/java/org/apache/wicket/core/request/mapper/MountedMapper.java
WICKET-4997: fix testcases

Conflicts:
	wicket-core/src/test/java/org/apache/wicket/TestDetachPageAjaxResult.html
	wicket-core/src/test/java/org/apache/wicket/ajax/AjaxHeaderContributionPage2_ajax_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/AjaxHeaderContributionPage2_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/AjaxHeaderContributionPage_ajax_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/AjaxHeaderContributionPage_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/DomReadyOrderPage_ajax_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/DomReadyOrderPage_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/form/AjaxFormSubmitTestPage_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/form/OnChangeAjaxBehaviorTestPage_expected.html
	wicket-core/src/test/java/org/apache/wicket/ajax/markup/html/componentMap/SimpleTestPageExpectedResult-1.html
	wicket-core/src/test/java/org/apache/wicket/markup/html/border/BoxBorderTestPage_ExpectedResult_11.html
	wicket-core/src/test/java/org/apache/wicket/markup/html/border/BoxBorderTestPage_ExpectedResult_3.html
	wicket-core/src/test/java/org/apache/wicket/markup/html/list/IncrementalTableNavigationPage_ExpectedResult_1.html
	wicket-core/src/test/java/org/apache/wicket/markup/html/list/PagedTablePageExpectedResult.html
WICKET-4997: more restrictive condition for using bookmarkable urls