Usability improvements for Extended Table Widget and SQL

results pane

Copy for multi-line text data surrounds the text with the
<pre> tag in the HTML version for avoiding line white-space
adjustments in the pasted text. See #1058

Do not use binary data in the "Use as Filter" option.

Indicate the existence of an error in the background of the
SQL results frame. The error-indicators is reused for
disabling this functionality.

When nothing is shown, a placeholder text hints the
objective of the results pane.

The preference label for the font size of this pane is
modified for consistency (SQL Log is another widget).

src/SqlExecutionArea.h

@@ -31,7 +31,7 @@ public:
     ExtendedTableWidget *getTableResult();
 
 public slots:
-    virtual void finishExecution(const QString& result);
+    virtual void finishExecution(const QString& result, const bool ok);
     virtual void saveAsCsv();
     virtual void saveAsView();
     virtual void reloadSettings();
@@ -54,6 +54,7 @@ private:
     QString sqlFileName;
     Ui::SqlExecutionArea* ui;
     bool m_columnsResized;              // This is set to true if the columns of the table view were already adjusted to fit their contents
+    bool showErrorIndicators;
 };
 
 #endif