add LESS support

still needs testing
added missing lessc library
fixed ini replacement to less variables stuff
lessyfied the first of template's CSS files
lessyfied another one
lessified more files
make sure calculations are correct
convert ini replacements to less vars first

This makes it possible to safely overwrite ini replacements from within
any less file
removed debug statement. sorry
fixed broken structure
unlessified and lessified a few more css
switched to LESS variables in rest of template's css files
removed possibility to have rtl.less files in plugins
FS#2751 - self deletion of user account
unit tests for self deleting of user accounts
de/de-informal: localization updates (delete user function)
Merge pull request #249 from lupo49/FS#2751

de/de-informal: localization updates (delete user function)
HTTPClient don't pull too much bytes when no content-length is given
coding corrections. correct type hint, remove unused variable assignment
Merge remote-tracking branch 'origin/FS#2751' into FS#2751