Fix tests so that they work in all screen sizes and resolutions.

Some tests in B2Qt RTA test suite don't work well when screen size and resolution are radically different. The biggest culprit is the way Squish accesses elements: on occasion, Squish can't find the elements and instead taps on a specific location specified in pixels. This leads to different results when the screen resolution is changed. This shuld be fixed so that tests always refer to elements by their name and not by their pixel offset.