Port StTable to StThemeNode

Convert the StTable code from StStylable to StThemeNode. The
:row-spacing and :col-spacing GObject properties are converted
into spacing-rows and spacing-columns style properties.

A new interactive test is added for StTable.

https://bugzilla.gnome.org/show_bug.cgi?id=596811

tests/interactive/table.js

@@ -0,0 +1,56 @@
+/* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */
+
+const Clutter = imports.gi.Clutter;
+const St = imports.gi.St;
+
+const UI = imports.testcommon.ui;
+
+UI.init();
+let stage = Clutter.Stage.get_default();
+stage.width = stage.height = 600;
+
+let vbox = new St.BoxLayout({ vertical: true,
+                              width: stage.width,
+                              height: stage.height,
+                              style: 'padding: 10px; '
+                                     + 'spacing: 10px;'
+                                     + 'font: 15px sans-serif;' });
+stage.add_actor(vbox);
+
+function L(text, color) {
+    return new St.Label({ text: text,
+                          style: "background: " + color + ";"
+                                 + "border: 1px solid rgba(0,0,0,0.5);"
+                                 + "padding: 1em;" });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+let table = new St.Table({ style: "border: 10px solid #888888;"
+                                  + "padding: 10px;"
+                                  + "spacing-rows: 5px;"
+                                  + "spacing-columns: 15px;" });
+vbox.add(table, { expand: true });
+
+table.add(L("1", "#ff0000"),
+          { row: 0, col: 0, col_span: 3 });
+table.add(L("2", "#00ff00"),
+          { row: 1, col: 0, row_span: 2 });
+table.add(L("3", "#0000ff"),
+          { row: 1, col: 1,
+            x_expand: 0 });
+table.add(L("4", "#ffff00"),
+          { row: 1, col: 2,
+            y_expand: 0, y_fill: 0
+          });
+table.add(L("5", "#ff00ff"),
+          { row: 2, col: 1, x_expand: 0 });
+table.add(L("6", "#00ffff"),
+          { row: 2, col: 2,
+            x_expand: 0, x_fill: 0, x_align: 1.0,
+            y_expand: 0, y_fill: 0, y_align: 1.0 });
+
+////////////////////////////////////////////////////////////////////////////////
+
+stage.show();
+Clutter.main();