Introduced a simpler layout style

Old style is still available by renaming style_full.less to style.less
Added a better toggle into debug_mode: shift+dblclick the version number
Refactored all debug/error setting code to own file
Removed unneeded test folder from commit
New debugmode file
New login and register  feature

NEW: login feature, ajax-based login function, with multiple languages
CHG: improved debug-mode, all visible at bottom if enabled
NEW: added login lang strings for login to DEU and FRA
CHG: removed all shadows; cleaner, flat look (Metro style-ish)
CHG: moved version info to very bottom, extra  links moved to help file
FIX: purge session function
CHG: english lang strings are default for missing items
FIX: various bugs in User class