inserted undo menu

did some little cleanup of code as well
function: undo

replaced the list of HistoryItems with list of pointers to these items, because that allows to do some really fast operations with them, cleaned up some other code too
improved

now it replaces the talk page of user with a welcome template in case you want to undo your rollback and talk was created
fixed

the revert query now revert only 1 revision in case we require that
split history items and fixed
travis phox
forgot this
performance optimization
optimized

some of these functions don't really need to be encapsulated so we can just directly include them in callers
login

there was an issue with loading of site info where information retrieved from previous query wasn't cleaned in case login was started multiple times
bug

for large screens the status bar can fuck up
followup
login crash
magic
give status bar some stretch
segfault on delete
Update core.cpp
more i18n
Localisation updates from https://translatewiki.net.
Merge pull request #63 from albebas/patch-4

Update core.cpp