libsysprof-gtk: add SysprofMarkTable

This is a raw view of the marks in a session which should help for just
finding the information you care about when the visual model is too
cumbersome or lacks searching capabilities.

src/libsysprof-gtk/style.css

@@ -62,3 +62,11 @@ callgraphview row:not(:selected) treeexpander symbol.unwindable {
   border-radius: 9999px;
   background-color: alpha(@error_color, .1);
 }
+
+marktable {
+  font-size: .9em;
+}
+
+marktable row:nth-child(odd):not(:selected) {
+  background-color: alpha(currentColor, .05);
+}