Fix issues launching fsck via terminal on Linux (#1086)

Currently on a system without xterm or konsole (like fresh
Ubuntu install) the fsck check will not launch. Added
gnome-terminal as an alternative and fixed an issue where
konsole will always error out as --title and --caption are
no longer valid arguments.

Previously the error message was simply "xterm not found", so
new LangString LINUX_EX2MSG_TERMINALNOTFOUND was added to let the
user knows which programs they need to get the feature working.

src/Main/Forms/WaitDialog.cpp

@@ -74,6 +74,7 @@ namespace VeraCrypt
 		VC_CONVERT_EXCEPTION (ParameterTooLarge);
 		VC_CONVERT_EXCEPTION (PartitionDeviceRequired);
 		VC_CONVERT_EXCEPTION (StringConversionFailed);
+		VC_CONVERT_EXCEPTION (TerminalNotFound);
 		VC_CONVERT_EXCEPTION (TestFailed);
 		VC_CONVERT_EXCEPTION (TimeOut);
 		VC_CONVERT_EXCEPTION (UnknownException);