tests: Add testdatatable

Add a GtkColumnView scrolling performance test similar to the one used previously in #3334 (closed).

The test creates a table with 20 columns and 10,000 rows and scrolls it to a random position every frame, while measuring the frame times.

There is a commandline flag to pick the cell widget between none (for benchmarking raw column view scrolling) and various label types. There is also a commandline switch to disable automatic scrolling in case a manual assessment is desired. Finally, there's an argument for controlling the number of columns.

cc @otte