- remove duplicate includes, that are already present in ui_optionsdialog.h
- change QIntValidator to not allow 0 as port-number
- re-order some function calls to match the Ui element order, for better readbility and to prepare for the addition of further IPv6 and Tor proxy options
- restat warning for the language selection is only shown, when the language was changed (not on simply activating the Ui element)
- split check for object == ui->proxyIp into seperate if-clause
- micro-optimize the code in the above mentioned if-clause
- unify used format for comments in the code
- introduce handleProxyIpValid() function, which handles UI elements and the
save button states for valid/invalid proxy IPs