[BUGFIX] Re-dispatch Content-length header after change
[TASK] Fully deprecate and ignore showHidden on menus

Field is a core enableField which should be respected. The PageRepository is being used and can (if we decide so in the future) be prepped to show hidden pages *if a BE user is logged in* or depending on other ENV.
[BUGFIX] Ensure types in condition
[BUGFIX] Use charset when formatting
[BUGFIX] Merge with add file and file reference properties
Merge pull request #554 from hmspl/merge

[BUGFIX] Merge with add file and file reference properties
Merge pull request #553 from hmspl/conv

[BUGFIX] Use charset when formatting
[BUGFIX] Don't re-dispatch content-length in debug mode
[BUGFIX] Menu vh must respect language_mode
Merge pull request #559 from hmspl/language_mode

[BUGFIX] Menu vh must respect language_mode
Merge pull request #558 from bjo3rnf/debugrendering

[BUGFIX] Don't re-dispatch content-length in debug mode
[BUGFIX] Allow sysfolder as subpages in vhs menu helpers
Merge pull request #560 from hmspl/sysfolder

[BUGFIX] Allow sysfolder as subpages in vhs menu helpers
Merge pull request #551 from bjo3rnf/submenufix

[BUGFIX] Expand submenus on active pages
[BUGFIX] Use page uid for overlay
Merge pull request #563 from FluidTYPO3/shortcut_overlay

[BUGFIX] Use page uid for overlay
[BUGFIX] Don't re-dispatch content-length with active BE sessions
Merge pull request #564 from bjo3rnf/debugrendering

[BUGFIX] Don't re-dispatch content-length with active BE sessions
[BUGFIX] No early return on empty menu in deferred rendering mode
Merge pull request #568 from bjo3rnf/deferredfix

[BUGFIX] No early return on empty menu in deferred rendering mode