[FEATURE] Attribute "as" on all menu ViewHelpers

Use of this argument allows setting the name of the variable that should contain the menu structure (note: in addition to the "menu" variable).
[TASK] Make property movable default to FALSE for CSS assets
[TASK] Make use of setter
[TASK] Typo in docblock
[TASK] Reorder getters and setters
Merge pull request #223 from NamelessCoder/as

[FEATURE] Attribute "as" on all menu ViewHelpers
Merge pull request #227 from bjo3rnf/movethatasset

[TASK] Add CSS assets to header by default
[BUGFIX] Relocate fetching of "as" on DeferredMenu
[BUGFIX] Respect argument showHidden when detecting subpages

Hidden pages (nav_hide=0) were always excluded from subpage detection even with showHidden=TRUE.
Merge pull request #229 from bjo3rnf/hiddenfix

[BUGFIX] Respect argument showHidden when detecting subpages