Command line option for running with some setting set to a given value

There are cases where the default configuration makes impossible to
use the application, due to some misbehaviour, like in issue #1560. This
new command line option allows users to set any setting to any value.
The setting is not saved unless user enters Preferences and saves the
current values. This allows overriding the preferences for the session
duration from the command line and also overriding the defaults for the
first session to work around problems with those defaults.

See issue #1588

src/Application.cpp

@@ -90,6 +90,7 @@ Application::Application(int& argc, char** argv) :
             qWarning() << qPrintable(tr("  -s, --sql [file]\tExecute this SQL file after opening the DB"));
             qWarning() << qPrintable(tr("  -t, --table [table]\tBrowse this table after opening the DB"));
             qWarning() << qPrintable(tr("  -R, --read-only\tOpen database in read-only mode"));
+            qWarning() << qPrintable(tr("  -o, --option [group/setting=value]\tRun application with this setting temporarily set to value"));
             qWarning() << qPrintable(tr("  -v, --version\t\tDisplay the current version"));
             qWarning() << qPrintable(tr("  [file]\t\tOpen this SQLite database"));
             m_dontShowMainWindow = true;
@@ -113,6 +114,22 @@ Application::Application(int& argc, char** argv) :
             m_dontShowMainWindow = true;
         } else if(arguments().at(i) == "-R" || arguments().at(i) == "--read-only") {
             readOnly = true;
+        } else if(arguments().at(i) == "-o" || arguments().at(i) == "--option") {
+            const QString optionWarning = tr("The -o/--option option requires an argument in the form group/setting=value");
+            if(++i >= arguments().size())
+                qWarning() << qPrintable(optionWarning);
+            else {
+                QStringList option = arguments().at(i).split("=");
+                if (option.size() != 2)
+                    qWarning() << qPrintable(optionWarning);
+                else {
+                    QStringList setting = option.at(0).split("/");
+                    if (setting.size() != 2)
+                        qWarning() << qPrintable(optionWarning);
+                    else
+                        Settings::setValue(setting.at(0), setting.at(1), option.at(1), /* dont_save_to_disk */ true);
+                }
+            }
         } else {
             // Other: Check if it's a valid file name
             if(QFile::exists(arguments().at(i)))