start working on multilingualism
restructure some code

still working on multilingualism
optimizations
element overhaul (WIP)
multilingualism (WIP)
multilingualism for categoryItems element type
minor template improvements
plain element type
reinsert i18n-values when editing a page
documentation improvements
documentation improvements
small code improvement
delayed deactivation of pages
re-add icons for element types
resolve some todos
set default values for settings through options
drop function to duplicate pages
remove 'countMenuItems'

function becomes unnecessary with upcoming changes to the menu system,
anyway.
support monolingual descriptions
add missing cache reset