- add enableApplyButton() and disableApplyButton() to optionsdialog.{h/cpp}
- they are used to ensure the Ok button does not get disabled, when Apply needs to be disabled (standard UX should allow Ok always to dismiss the dialog and only disable it, when we have a faulty proxy IP)
- disable Apply after initially loading the settings, as nothing new needs to be saved
- remove orphan settings from optionsdialog.ui that are default anyway
- 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
- extend network options with a SOCKS version selection
- changing "Unit to show amounts in:" now also updates the unit used in the transaction fee box
- string updates
- link Apply button and OK button when enabling or disabling them
- use LookupNumeric() from netbase to verify proxy address (via an EventFilter)
- change proxy address field to QValidatedLineEdit and add visual feedback
- add a status label used for displaying a message for invalid proxy addresses
- allow usage of IPv6 address as proxy address
- added warning message when enabling / disabling SOCKS proxy
