Visual sort indicators for multi-column sorting (#1810)

This adds visual sort indicators to the already working multi-column
sorting. Qt sort indicator is disabled, so only one indicator per column
is visible.

Unicode characters are used to indicate direction (triangles) and sort
column order (superscript numbers).

See issue #1761

src/MainWindow.cpp

@@ -749,9 +749,6 @@ void MainWindow::populateTable()
         for(int i=1;i<m_browseTableModel->columnCount();i++)
             ui->dataTable->setColumnWidth(i, ui->dataTable->horizontalHeader()->defaultSectionSize());
 
-        // Sorting
-        ui->dataTable->filterHeader()->setSortIndicator(0, Qt::AscendingOrder);
-
         // Encoding
         m_browseTableModel->setEncoding(defaultBrowseTableEncoding);
 
@@ -849,15 +846,6 @@ void MainWindow::applyBrowseTableSettings(BrowseDataTableSettings storedData, bo
     for(auto widthIt=storedData.columnWidths.constBegin();widthIt!=storedData.columnWidths.constEnd();++widthIt)
         ui->dataTable->setColumnWidth(widthIt.key(), widthIt.value());
 
-    // Sorting
-    // For now just use the first sort column for the sort indicator
-    if(storedData.query.orderBy().size())
-    {
-        ui->dataTable->filterHeader()->setSortIndicator(
-                    storedData.query.orderBy().front().column,
-                    storedData.query.orderBy().front().direction == sqlb::Ascending ? Qt::AscendingOrder : Qt::DescendingOrder);
-    }
-
     // Filters
     if(!skipFilters)
     {